We found 15 cross‐sectional,3, 7-12, 19-26 two case–control,27, 28 and four prospective cohort29-32 studies, as summarized in Table 1.

Cross‐sectional studies

Population‐based studies suggest that acne prevalence is lower in rural societies than in industrialized populations. Cordain et al.19 studied the Kitavan islanders of Papua New Guinea (n = 1200) and the Aché hunter‐gatherers of Paraguay (n = 115). The islanders subsisted mainly on root vegetables, fruit, fish, and coconut. Their intake of dairy products, coffee, alcohol, cereals, oils, sugar, and salt was minimal. An estimated two‐thirds of the Aché hunter‐gatherer diet consisted of sweet manioc, peanuts, maize, and rice. Approximately one‐quarter of their diet consisted of flour, sugar, and meat. No cases of acne were detected in either population. The authors suggested that the low fat intake and the absence of high‐glycemic‐index foods may explain the low prevalence of acne in these populations.

Freyre et al.20 compared acne prevalence in three Peruvian populations, including indigenous and white populations (n = 2214). Among 12–18‐year‐olds, the indigenous population showed a significantly (P < 0.001) lower acne prevalence (28%) than the white population (45%) or those of mixed ancestry (43%). Each adolescent group had a lower prevalence of acne than that reported in 12–18‐year‐old Americans.20

Bechelli et al.21 assessed the prevalence of acne in 9955 Brazilian schoolchildren: 8980 were impoverished urban children, whereas 975 were from rural areas. Less than 3% of the combined population (2.7%) demonstrated evidence of acne.

Two reports have suggested that acne prevalence increases as populations adopt a Western diet through migration or cultural change. Reports of northern Canadian Inuits made no mention of acne until acculturation with their southern neighbors and subsequent increases in soda, beef, dairy products, and processed foods, after which the acne prevalence increased.22 Pre‐World War II Okinawans, who traditionally followed a diet of sweet potatoes, rice, and vegetables, together with some soybeans, but little meat, reported an increase in acne prevalence after adopting a diet high in animal products.23

Seven studies have assessed the perceptions of factors believed to affect acne.3, 7-12 In a 2007 study, Rigopoulos et al.7 assessed the beliefs about acne among 13–18‐year‐old Greek students with and without acne. Self‐reported acne was present among 59% of students. Among 316 students with and without acne, 62% cited diet as a causal factor, and 66% believed chocolate was an exacerbating factor. In 2006, El‐Akawi et al.10 reported that, of 166 Jordanian male and female untreated clinic patients with acne, participants believed that their acne was aggravated by nuts (89%), chocolate (85%), cakes/biscuits (57%), oily food (53%), fried food (52%), eggs (42%), or milk, yogurt, and cheese (23%). Nearly one‐fifth (19%) believed that consuming fruits and vegetables improved their acne. A survey administered by Ikaraoha et al.11 to 174 Nigerian students aged 18–32 years demonstrated that 75% of participants believed that an oily or fatty diet contributed to their acne. Of 130 male and female Saudi Arabian patients attending an acne clinic, more than one‐quarter of participants believed that diet caused (26%) or exacerbated (32%) their acne.8 A 2003 study9 of Saudi Arabian high school and college students (n = 517), aged 15–29 years, demonstrated that 72% of students with and without acne (and 79% of 217 students with acne) believed that diet contributed to acne. In a 2001 study in the Journal of the American Academy of Dermatology, Tan et al.3 reported that acne was believed to be caused by diet less frequently than by hormonal or genetic factors. Although 32% of acne patients believed that diet caused their acne, 64% believed that hormones and 38% believed that genetics were responsible. In addition, 44% of participants believed that diet aggravated their acne. In 2001, Green and Sinclair12 reported that almost half of 215 sixth‐year Australian medical students believed that diet aggravated their patients’ acne, citing chocolate and oily or fatty foods as the most common dietary factors.

Kaymak et al.24 examined the association between acne and the glycemic index and glycemic load of the daily diet, insulin sensitivity, and insulin‐like growth factor (IGF) levels in 91 university students (n = 49 acne patients, n = 42 control patients). Participants completed a food frequency questionnaire from which the authors calculated the glycemic index using published reports. Physicians assessed acne as well as insulin resistance through the calculation of the homeostatic model assessment (HOMA) index: [fasting insulin (microU/mL) × fasting blood glucose (mmol/L)/22.5]. There were no significant differences in fasting glucose or insulin levels, and none of the participants had insulin resistance. In patients with acne, levels of IGF‐1 were higher and levels of IGF‐binding protein‐3 were significantly lower than those of controls. Participants with acne of more than 2 years’ duration ate a diet with a significantly higher glycemic index than did participants with acne of less than 2 years’ duration.

Khanna et al.25 studied energy, carbohydrate, protein, and fat intake among 200 students in India with and without acne. They compared the diets of those with severe, moderate, mild, and no acne, and reported no dietary differences (P > 0.05) among the four groups; however, the researchers used a t‐test, intended for the comparison of two groups, rather than the appropriate analysis of variance statistical test to compare the four groups. It is unclear whether the results from appropriate statistical tests would have differed from those reported.

In a 1956 study published in the British Medical Journal, Bourne26 found that adult British soldiers, aged 20–40 years, with acne were significantly heavier than those without acne (73.2 kg vs. 67.5 kg; P = 0.013). Adolescent British soldiers aged 15–19 years with acne weighed more than those without acne (62.7 kg vs. 60.5 kg), although the differences were not significant.