Although laundering should mainly remove stains and dirt from used and worn textiles, the elimination of microbial contamination is an important aim of the laundry process as well. While industrial and institutional laundering employs standardized processes using high temperatures (i.e. 60°C and above) and bleaching agents to ensure a sufficient hygienic reconditioning of textiles, domestic laundering processes are less defined and not always led by purposeful aims. The strive for energy efficiency of household appliances has resulted in a decrease in washing temperatures in Europe during the last decades and convenience aspects led to an increased use of liquid detergents that do not contain bleach which in turn impacts the antimicrobial efficacy of domestic laundering. This review compiles the different factors that influence the input and removal of micro‐organisms in the laundering process and discusses the possible adverse effects of microbial contaminants in the washing machine and on the textiles as well as suitable counteractions.

Introduction Laundering mainly aims to remove visible stains but should also provide a hygienically clean textile surface, which means that microbial contamination and malodorous substances are removed as well. However, while the successful dirt removal can be assessed visually, the removal of micro‐organisms or malodours cannot be proven that easily. In the industrial and institutional setting, the cleaning as well as the hygiene performance of laundering is normally ensured by standardized processes which normally disinfect contaminated textiles via a combination of temperatures of at least 60°C and oxidizing agents (such as chlorine or activated oxygen bleach, AOB) (Gebel et al. 2001; Anon. 2013). In the domestic setting, however, the cleaning performance of the laundry process or the energy efficiency of appliances has proven to be of great importance to the consumer, while the hygienic effect of laundering is regarded as less important or even taken for granted as soon as the textiles are visually clean (Arild et al. 2003). Moreover, striving for energy efficiency in laundry has led to a continuous decrease in the washing temperatures, which in turn impairs the antimicrobial performance, since temperature is one of the most important means to inactivate micro‐organisms in the washing process (Honisch et al. 2014). For example, in Germany the mean washing temperature used for domestic laundry decreased from 63°C in 1972 to 46°C in 2014. In terms of temperatures used this means that the percentage of treatments ≥60°C has dropped from 62% in 1972 to 33% in 2014 (Industrieverband Körperpflege‐ und Waschmittel 2014). Although washing at 40°C instead of 60°C allows for a reduction in the energy costs of almost 50% (Industrieverband Körperpflege‐ und Waschmittel 2014), it has been shown that the complete inactivation of several types of micro‐organisms, such as Norovirus or fungi can only be achieved at temperatures >40°C (Ossowski and Duchmann 1997; Honisch et al. 2014; Lemm et al. 2014). The wash cycle time in programmes that use lower temperatures to improve energy efficiency has been prolonged to ensure the same cleaning result, which has been shown to work well for stain removal (Janczak et al. 2010), but only to a limited extent for the inactivation of micro‐organisms (Honisch et al. 2014). One of the biggest challenges when trying to evaluate the hygiene efficacy of domestic laundry processes is the lack of consistent data in the literature. Many studies have been performed according to standards and hygiene requirements of institutional or industrial applications such as hospital laundry which cannot be easily transferred to areas where the hygiene demands are different. Moreover, the need to remove or inactivate micro‐organisms in the domestic setting is not only substantiated by the aim to reduce a potential infection risk but also includes other adverse microbial effects such as malodour formation. On the other hand, the safe use of harmful chemicals and biocides by an unskilled end‐consumer requires other provisions than for the professional user and there is need for balancing aims such as hygiene, energy efficiency and cleaning performance. Therefore, it is important to understand the microbiological as well as other impact factors to be able to develop and implement adequate solutions and to educate the consumer appropriately.

Micro‐organisms on textiles Although the interaction between micro‐organisms and a textile surface depends on many parameters and may vary immensely, the process of wearing or using a textile followed by reconditioning in terms of sorting, laundering, drying and storing can be regarded as different means by which various microbial species are introduced to the fabric on the one hand and being mechanically removed from it or inactivated or killed on the other (Fig. 1). Every time when wearing a garment or using a textile, micro‐organisms will be transferred from the skin to the fabric. The extent of this transfer is likely to be dependent on the area of the body which the textile is in contact with as well as situation‐specific factors. For example, microbial transfer rates from armpits, especially in hot conditions are likely to be high, whereas general contaminations by members of the skin microbiota are assumedly lower. Some studies reporting the contamination of clothing in healthcare facilities suggest that frequent contaminations with micro‐organisms resistant to desiccation (such as Staphylococcus aureus) must be considered likely (Howe et al. 1961; Smith et al. 1987; Bloomfield et al. 2011) and that the total bioburden on items such as soiled sheets and terry towels (depending on certain situation‐dependent factors) might be up to 104–106 CFU per cm2 (Blaser et al. 1984). In contrast, there are virtually no investigations on the number of microbial cells and the composition of the microbiota on worn or used textiles in daily life scenarios, but some studies suggest that the microbial count after normal use might be in the range of 102–104 CFU per cm2 (McQueen et al. 2007; Lucassen et al. 2013, 2014). Interestingly, this number is considerably lower than the initial count that is used in normative experimental designs for the evaluation of the antimicrobial efficacy of laundering, which normally requires textile test carriers that have been artificially contaminated with up to 108 CFU per ml (Gebel et al. 2001; Anon. 2013) and thus might rather reflect a healthcare‐related situation. Although these test scenarios have been developed for the medical area they are widely used to prove the efficacy of domestic laundering as well, which leads to the question if these high levels of contamination are representative for this type of application. Likewise, the normative tests also use blood as an interfering substance, which does not resemble a type of soil typical for the nonmedical area. However, the nature of the organic soil that embeds the microbial cells on the textile might exert a huge influence on the means by which the contaminating microorganisms are removed or inactivated during laundering. For instance, Block et al. (2001) showed that the addition of organic soil in a washing machine test decreased the antimicrobial efficacy by c. 2–3 orders of magnitude. Figure 1 Open in figure viewer PowerPoint 2011 Input and removal of micro‐organisms during laundry‐related processes. After Bockmühl (). As for the amount of microbial cells, there are few investigations of the microbial species that can be found on textile surfaces. Nevertheless, two major sources of contaminants have to be considered with regard to laundry. The human body serves as the first source, not only by the skin microbiota or skin pathogens which can be transferred to the textile during wearing or usage but also when textiles are eventually sullied with other potentially contaminated matrices, such as faeces, blood or vomit, resulting in a broad variety of human‐related micro‐organisms that can be putatively found on textiles. Therefore, the antimicrobial efficacy of laundering is normally evaluated by considering different types of micro‐organisms, including Gram‐positive and Gram‐negative bacteria, fungi and viruses. The second major source of microbial contaminants is the environment and the washing machine itself. It has been shown that laundering does not only reduce the amount of microbial cells on the textile but sometimes even introduces micro‐organisms to a considerable extent (Lucassen et al. 2014). This phenomenon might be more pronounced if the washing machine is poorly maintained or if lower temperatures are used, but may also occur at higher washing temperatures, even at 90°C (Bellante et al. 2011; Lucassen et al. 2014). This can be (at least partly) explained by the fact that the rinse cycles are able to transfer microbial cells from the detergent distribution system of the washing machine to the textiles (even if they have been decontaminated in the main wash beforehand), which is virtually always colonized by microbial biofilms (Bockmühl 2011). Some studies investigating the composition of the microbiota on textiles and in washing machines, have suggested that a mixture of skin‐associated bacteria and ubiquitous micro‐organisms from the environment and from machine biofilms may comprise the relevant microbial community associated with laundry (Blaser et al. 1984; Smith et al. 1987; Gattlen et al. 2010; Babic et al. 2015; Callewaert et al. 2015; Nix et al. 2015). In this regard, it can be assumed that the laundering process causes a shift in the microbial community on the textiles from primary contaminants (e.g. skin bacteria) to secondary contaminants (e.g. biofilm‐associated environmental bacteria) (Bellante et al. 2011; Callewaert et al. 2015). Table 1 compiles some typical genera present on textiles and in the washing machine. In addition, other micro‐organisms, such as pathogens, may be relevant under special circumstances. For instance, it must be assumed that contaminations with dermatophytes, viruses and faecal pathogens may occur when family members suffer from the respective diseases. Table 1. Typical laundry‐associated micro‐organisms found on textiles and in the washing machine and their possible sources. The possible sources were assigned based on the microbial genera and locations described in the referenced articles. Selected from indicated references: 1 (Callewaert et al. ); 2 (Nix et al. ); 3 (Gattlen et al. ); 4 (Smith et al. ); 5 (Blaser et al. ); 6 (Babic et al. ) Genus Classification Presence Possible source Reference Textile Machine Environment Human Acinetobacter Gr− bacteria x x x x 1, 2, 6 Brevundimonas Gr− bacteria x x x 1, 2, 6 Candida Yeast x x x 2, 5, 6 Citrobacter Gr− bacteria x x 3 Cladosporium Mould x x 2, 6 Corynebacterium Gr+ bacteria x x 1 Enhydrobacter Gr− bacteria x x 1 Enterobacteriaceae Gr− bacteria x x x 2, 3, 4, 5 Enterococcus Gr+ bacteria x x x 4 Flavobacterium Gr− bacteria x x x 1, 2 Fursaium Mould x x 2, 6 Microbacterium Gr+ bacteria x x 2, 3, 6 Micrococcus Gr+ bacteria x x x 1, 6 Ochrobactrum Gr− bacteria x x 2, 6 Propionibacterium Gr+ bacteria x x 1 Pseudomonas Gr− bacteria x x x 1, 2, 3, 4, 5, 6 Rhodotorula Yeast x x 2, 3, 6 Staphylococcus Gr+ bacteria x x x 1, 3, 4, 5

Factors influencing the hygiene efficacy of laundering To explain the influence of parameters determining the cleaning performance in laundry, the Sinner circle has long been used and is widely accepted (Sinner 1960). This concept states that the four factors, time, temperature, mechanical action and chemistry, work together in the cleaning process. Each of the factors accounts for a certain percentage of the total cleaning performance and can in principle be compensated by one of the other three. One of the most prominent examples for the application of this concept can be found with the ‘eco’‐programmes of current washing machines that aim to decrease the washing temperatures in order to save energy and exhibit in turn very long programme durations. This has been shown to work very well in terms of soil removal. The same cleaning performance can, for example, be achieved when using a standard programme at 60°C or an extended programme at 40°C (Janczak et al. 2010). It has also been established that temperature is one of the most important factors to ensure laundry hygiene. Although it is difficult to differentiate between the Sinner circle impact factors in many of the existing studies it is obvious that a higher washing temperature increases the logarithmic reduction (LR) of micro‐organisms on a textile surface during laundering. Wiksell et al. (1973) observed an LR increase of c. 2·5 when shifting the temperature from 24°C to 68°C while Walter and Schillinger (1975) found the LR to be increased by 3 by raising the temperature from 38°C to 49°C. These studies were followed by many others showing a considerable effect of temperature on the reduction of micro‐organisms (Arild et al. 2003; Lichtenberg et al. 2006; Bellante et al. 2011; Linke et al. 2011; Honisch et al. 2014). Most of these investigations suggest that a temperature of above 50°C would deliver a significant LR, although the impact may vary with the chosen conditions and with the selected test microbes. Along with temperature, chemistry is regarded as the second most important factor that influences the antimicrobial efficacy of laundering processes. However, the laundry detergents used can be made up of many different components, making it very difficult to estimate the impact of a certain compound or to compare different studies. Nevertheless, there are three major groups of ingredients that may determine the antimicrobial efficacy of detergents: surfactants, bleaching agents and quaternary ammonium compounds. Surfactants as the most important component of detergents account for the basic cleaning efficacy and should remove hydrophobic soil. There are only few investigations that allow observation of this detergency effect of surfactants on micro‐organisms. Honisch et al. (2016) recently investigated laundry processes with and without detergents and found little or no effects when comparing the remaining microbial load on artificially contaminated swatches after laundering in a domestic washing machine. Only S. aureus (and to a lesser extent Enterococcus hirae) exhibited a considerably higher LR when washed with detergent compared to water alone, probably due to a better removal of bacterial cells from the fabric, since suspension tests virtually show no antimicrobial effects when detergents are added (Brands et al. 2016). In comparison with surfactants, bleach has to be considered the major antimicrobial active ingredient in laundering processes. The use of bleach, however, varies greatly within different regions of the world. First of all, the term ‘bleach’ may refer to chlorine bleach (sodium hypochlorite) that is traditionally added to the laundry, for example, in southern Europe or the United States. Consumers in other countries, such as Germany, prefer to use AOB—mainly peracetic acid derived from perborate or percarbonate and the bleach activator tetraacetylethylenediamine (TAED). In contrast to chlorine bleach, AOB can be formulated into solid detergents using the precursor substances, thus resulting in a product which is convenient to use and provides good cleaning results even at lower temperatures. In special products and in industrial laundering, other oxidizing agents, such as hydrogen peroxide or phthalimidoperoxyhexanoic acid are used as well. This chemical diversity makes it difficult to assess the antimicrobial impact of bleach when reviewing the scientific literature, because many of those studies do not disclose what kind of bleaching agents was used. Nevertheless, nearly all of these investigations show that AOB or chlorine bleach can enhance the antimicrobial activity of detergents significantly. Experimental studies that compared detergents with and without AOB suggest that the additional LR due to AOB might range from 2 to 6, but these values may vary with the chosen conditions (e.g. temperature, time, etc.) and the tested organisms (Arild et al. 2003; Lichtenberg et al. 2006; Linke et al. 2011; Honisch et al. 2014, 2016). Interestingly, although the TAED‐mediated activation of percarbonate or perborate is temperature‐dependent and should work best at temperatures of above 40°C, an additional antimicrobial effect can already be observed at lower temperatures (Honisch et al. 2014). Likewise, chlorine bleach was shown to enhance the antimicrobial efficacy of laundering by 3–4 orders of magnitude, even at low temperatures (Walter and Schillinger 1975; Christian et al. 1983; Blaser et al. 1984; Smith et al. 1987). Apart from bleach (AOB or chlorine bleach), quaternary ammonium compounds—mainly benzalkoniumchloride (BAC) and didecyldimethylammoniumchloride (DDAC)—are used as antimicrobial actives for laundering processes. Due to their cationic nature, these compounds are incompatible with anionic surfactants, which, however, can be found in virtually any current market detergent. Therefore, quaternary ammonium compounds cannot be used in the main wash together with the laundry detergent, but have to be dosed afterwards during rinsing, resulting in some consequences. Cationic surfactants, like quaternary ammonium compounds, can interact with the textile surface, if the textile polymers (e.g. cellulosic fibres) are negatively charged or at least electronegative. This phenomenon is also used in fabric softeners, which contain cationic surfactants as well, building a layer on the fibres and thus softening their surface. So it must be assumed that cationic surfactants at least partly stay on the fibres even after laundering, providing a sustainable antimicrobial effect. Considering the fact that these products are applied after the main wash, they might also help to reduce the microbial burden of secondary contaminants (as mentioned above) originating from machine biofilms. Machine‐related microbial contamination was revealed in studies using consumer‐owned washing machines (Bellante et al. 2011; Lucassen et al. 2014). This can be (at least partly) compensated by the use of rinse‐aids (hygiene rinsers) containing BAC or DDAC (Lucassen et al. 2013). Although these products thus may help to enhance the hygiene efficacy of laundering (especially with delicate laundry that may not be washed with bleach) they have to be used in a prudent way, since it has been shown that quaternary ammonium compounds can promote resistances against biocides and perhaps even against antibiotics (Lambert 2004; McCay et al. 2010). While the impact of temperature and chemistry has been subject to numerous studies, the influence of time and mechanics has not been investigated nearly so intensively. These two parameters have to be considered interdependent, since the prolongation of the wash cycle time results in more mechanical action (but will also increase the influence of chemistry and temperature). Honisch et al. (2014) systematically investigated the effect of main wash times on the antimicrobial efficacy of laundering and found that prolonged main wash times can increase the LR of the tested organisms significantly, especially when detergents without AOB were used. However, unlike the use of AOB, the prolongation of the wash cycle time did not result in the complete elimination of micro‐organisms on artificially contaminated swatches at temperatures below 50°C. Therefore, it must be assumed that prolongation of time can only partly compensate for decreasing temperatures as suggested by the Sinner circle. To assess the impact of mechanics on the antimicrobial efficacy of laundering, Brands et al. (2016) performed suspension tests and compared the data with test results obtained in a washing machine using similar chemistry and temperatures. It was shown that the reduction of microbial cells on a textile surface during laundering at 20–40°C must be considered a physical removal effect rather than an inactivation by temperature or surfactants. At higher temperatures or when bleach is used, it can be assumed that the microbial cells are being inactivated by these means as well. Interestingly however, for most of the tested bacterial and fungal organisms (S. aureus, E. hirae, Pseudomonas aeruginosa and Candida albicans but not for Trichophyton mentagrophytes) it was not possible to achieve a complete reduction using AOB without mechanical action. This means that the removal of microbial cells (mediated by the drum agitation and the physicochemical interaction with surfactants) plays an important role in laundry hygiene also at higher temperatures. Apart from the parameters covered by the Sinner circle, there are numerous other factors that may affect the hygiene efficacy of laundering, none of which has been subject to comprehensive investigation. Some factors that should be mentioned (without intending to be exhaustive) are the type of textile (e.g. cotton, polyester, wool), the soil matrix in which the micro‐organisms are embedded on the fabric (e.g. blood, faeces, food) and the conditions surrounding the laundering process (e.g. drying). There are some indications that these parameters may also play an important role in laundry hygiene. For example, micro‐organisms colonize various types of textile differently. Teufel et al. (2010) showed that the colonization patterns of human skin bacteria on polyester, cotton, polyamide and polypropylene textiles differed qualitatively and quantitatively after a 24‐h incubation period in a human sweat sample. Moreover, the type of soil in which the micro‐organisms are embedded on the textile might affect their removal by surfactants and mechanical action or might even suppress oxidative agents such as bleach. Although the latter effect is considered by adding organic substances in the experimental setup (usually bovine serum albumin or defibrinated sheep blood) there are no systematic investigations on how different soil matrices might affect laundry hygiene.

Efficacy of laundering against different groups of micro‐organisms One of the basic principles in antimicrobial efficacy testing is the use of test strains from different representative and relevant groups of micro‐organisms. The European standard for chemical–thermal textile disinfection, which should be applied in areas where disinfection is necessary (i.e. nursing homes, hospitals, hotels, food processing premises etc.), requires the testing of bacteria (P. aeruginosa, Escherichia coli, S. aureus, E. hirae), yeasts (C. albicans) and—if applicable—mould (Aspergillus brasiliensis) and mycobacteria for laundry processes below 60°C. For laundry processes ≥60°C, only Enterococcus faecium must be tested (Anon 2013). Although this selection of strains is reasonable for most of the application areas listed above, testing for other organisms may be required in some cases as well. It should be considered in this regard that areas such as the domestic setting may require lower rates of inactivation, since there might be no need to apply the same amounts of chemicals or energy. Concerning the different groups of micro‐organisms, bacteria are probably the most frequent organisms tested. It is, however, not easy to make a general statement about the antibacterial efficacy of laundering, since this group is very diverse. Nevertheless, it can be assumed from several studies that most bacteria (except for heat‐resistant strains) are inactivated very well even at lower temperatures when AOB is used (Lichtenberg et al. 2006; Linke et al. 2011; Honisch et al. 2014). Laundering without AOB seems to be more effective against Gram‐negative bacteria, perhaps due to the presence of an outer cell membrane that might be more prone to detergent attacks (Honisch et al. 2014). Bacterial spores are known to be more resistant than vegetative cells and have to be considered as relevant contaminants especially in the hospital environment, where spore‐forming bacteria such as Clostridium difficile might pose a problem. It was shown, that C. difficile could be isolated from the bed linen of patients with a positive stool toxin test even after laundering at 71°C (Lakdawala et al. 2011). Since viral infections are among the most common infections in the everyday life setting, providing effectiveness against viruses is crucial for laundering processes. Viral pathogens include enteric viruses (such as norovirus and rotavirus), respiratory viruses (e.g. influenza) and others such as herpesvirus and poliovirus. In terms of the antiviral efficacy of laundering it appears most important whether the viral particle is enveloped or nonenveloped. Several studies suggest that laundering is more effective against enveloped viruses, most probably because the phospholipid envelope can be disrupted by the detergent (Sidwell and Dixon 1969; Gerba 2001; Gerba and Kennedy 2007; Gerhardts et al. 2009; Heinzel et al. 2010). Again, bleach (AOB or chlorine bleach) does considerably improve the antiviral efficacy during laundering, but only when temperatures of 60°C or higher are used, can the complete inactivation of nonenveloped viruses such as poliovirus or norovirus be assured (Heinzel et al. 2010; Lemm et al. 2014). Interestingly, although viral infections must be considered very relevant for laundry hygiene, efficacy testing mostly focuses on bacteria (Anon 2013). Effectiveness of laundering against fungi must be also considered very important. Fungal infections are common in developed countries and contaminated textiles may serve as vectors. Socks worn by patients with dermatomycoses can carry huge amounts of fungal cells and spores and may spread the infection, since the infectious dose of dermatophytes is often very low (Hammer et al. 2011). In patients with vaginal candidiasis it is believed that contaminated underwear might cause reinfections even after successful therapy (Duchmann et al. 1999). To eliminate these fungal pathogens from contaminated textiles, data suggest that higher temperatures and the use of bleach is needed for complete inactivation (Hammer et al. 2011; Honisch et al. 2014). Taken together, laundering below 60°C without AOB or chlorine bleach does not guarantee efficacy against all kinds of micro‐organisms. Only higher temperatures and the use of bleaching agents can probably ensure the sufficient decontamination of textiles, especially in critical cases, such as dermatomycoses or gastrointestinal infections.

Adverse microbial effects associated with laundering Although most of the published studies dealing with laundry hygiene emphasize the control of infections that might be attributed to insufficiently decontaminated textiles, it must be considered that there are other adverse effects related to micro‐organisms and laundry. Especially in the domestic environment, malodour formation is probably regarded as one of the most prominent microbiological problems and might put a considerable pressure on affected people. In some cases, malodorous laundry can be linked with insufficiently removed traces of sweat. The sweat ingredients might serve as nutrient for remaining bacteria that are able to grow and metabolize the sweat compounds if the humidity is high enough (Munk et al. 2001; Teufel et al. 2010; Denawaka et al. 2016). As mentioned before, the type of textile has a great influence on the qualitative and quantitative occurrence of both sweat molecules and micro‐organisms (Teufel et al. 2010). Interestingly, the absolute numbers of bacteria that can be found on a certain type of textile does not necessarily correlate with the formation of malodour (McQueen et al. 2007), which might be explained by a different composition of the colonizing microbiota or an unequal affinity of the malodorous substances to the various textile polymers. A second malodour problem associated with laundering does not seem to be related to sweat and the skin microbiota but might rather be caused by micro‐organisms colonizing the washing machine. Kubota et al. (2012) reported a ‘wet‐and‐dirty‐ dustcloth‐like malodour’ appearing directly after laundering and proposed that this type of malodour might be caused by Moraxella species, a Gram‐negative bacterium that can colonize the washing machine. Although Moraxella is not among the most commonly isolated bacteria from washing machine biofilms in Europe and thus might be a problem more relevant in Asia (Gattlen et al. 2010; Callewaert et al. 2015; Nix et al. 2015), it appears likely that biofilm‐forming organisms cause malodour when distributed onto the textiles after the main wash (Bellante et al. 2011; Lucassen et al. 2014). Although this type of malodour might be as common as the formation of sweaty odour, little is known about the malodorous substances or the way they are formed. Takeuchi et al. (2012) proposed C7‐branched fatty acids to be mainly responsible for this phenomenon, which is interesting, because these molecules are quite similar to those that are present in human sweat after bacterial metabolization (Natsch et al. 2003; Emter and Natsch 2008). Biofilm formation is another adverse effect of microbial colonization and a widespread phenomenon in water systems, known to be a source of technical problems, such as obstructions and corrosion (Coetser and Cloete 2005) and a potential reservoir of pathogens (Wingender 2011). Nix et al. (2015) analysed biofilms using molecular methods on different washing machine surfaces, such as the detergent drawer and the rubber sealants and found the microbial community to be very diverse, consisting of fungi and bacteria many of which are known as biofilm‐forming organisms. It remains unclear, however, to which extent these strains may cause technical problems or pose a considerable health risk. When trying to estimate the potential infection risk associated with laundering, numerous aspects have to be considered. Most importantly, the pathogenic micro‐organisms themselves and their potential routes of transmission and infection have to be taken into account. As mentioned above, there are two major groups of micro‐organisms associated with laundry: environmental fungi and bacteria (for which the washing machine might serve as a reservoir) and microbes related to the human body (primarily brought into the laundry via contaminated textiles). However, many harmful pathogens associated with laundry will probably not pose a considerable risk of infection, either because they are readily inactivated during the laundering process (e.g. enveloped viruses, such as influenza) or there is no probable infection route (e.g. in the case of faecal‐oral infections). This assessment might differ of course, when people of higher risk (young, old, pregnant or immunocompromised) are involved, which would call for a higher level of hygiene in domestic and institutional laundry. These considerations may hint at some pathogens of particular interest, for which a laundry‐related risk of infection can be anticipated. These micro‐organisms include dermatophytes and yeasts (e.g. Candida) which can be transmitted directly via insufficiently decontaminated textiles, gastrointestinal bacteria and viruses (such as Norovirus), especially if their infectious dose is low and possibly other nosocomial and facultative pathogens (e.g. MRSA) which may represent a threat to predisposed persons, such as immunocompromised patients, young children, pregnant women and elderly people. This list must not be considered complete; instead, the level of hygiene related to laundering should be adjusted to the respective situation and need by exploiting the influencing parameters described above. To estimate exactly what risk is associated with contaminated laundry, it would be necessary to consult epidemiological studies. However, there are very little data available that relate laundering habits to a related infection risk. A comprehensive analysis of the relevant data was carried out by Bloomfield et al. (2011), who also assessed the potential risk from exposure to contaminated textiles relative to other fomites at home, such as hands and domestic surfaces. It was concluded that contaminated fabrics may pose a potential health risk by carrying pathogens from a variety of sources at home, although the risk of infection associated with other transmission routes (e.g. via hands or food‐contact surfaces) was considered higher. Nevertheless, the authors identified more than 15 case studies and observational reports in which clothing items or linen were likely to be the source of infection. These reported cases include outbreaks caused by bacteria, for example, Staphylococci (Payne 1959; Nguyen et al. 2005) and Streptococci (Brunton 1995), viruses (St Sauver et al. 1998) and dermatophytes (Shah et al. 1988). Moreover, Larson and Duarte (2001) investigated the relationship between home hygiene practices and the prevalence of infections in family members and found that using a communal laundry without using bleach was highly predictive of an increased infection risk. An interesting approach to estimating the infection risk associated with laundering is the use of quantitative microbial risk assessment (QMRA), used by Gibson et al. (1999) who calculated that the probability of acquiring a Shigella infection via contact with contaminated clothing could be reduced by 90% through laundering.

Conclusion Laundering can help to break the chain of infection transmission in domestic as well as healthcare settings by either removing pathogens from the textile surface or inactivating them by the means of chemistry and temperature. It has been shown that contaminated laundry may pose a possible health risk and may also be a source of other problems, such as malodour. However, since there is a constant striving for energy efficiency, especially with household appliances, the use of lower washing temperatures must be traded off against the hygiene efficacy of laundering which is considerably influenced by the temperature profile. Likewise, the prudent use of antimicrobial actives (such as AOB) can help to ensure a suitable antimicrobial action of the laundering process, where this is needed, for example, when household members suffer from relevant infections or when immunocompromised persons are affected.

Acknowledgements The author thanks Sally Bloomfield for providing insight and expertise and Conor Watson for critical reading and correction of the manuscript.

Conflict of Interest No conflict of interest is declared.