Rosacea (Image: Dr Harout Tanielian/Science Photo Library) Demodex mite in the face of an adult (Image: Kevin Kavanagh/NUI Maynooth) Demodex mites extracted from the face of a rosacea sufferer (Image: Kevin Kavanagh/NUI Maynooth)


There are tiny bugs closely related to spiders living in the pores of your face. They have long been considered mere passengers, doing no harm beyond upsetting the squeamish. But they may be causing an ancient skin disease that is estimated to affect between 5 and 20 per cent of people worldwide, and 16 million in the US alone.

People aged between 30 and 60, especially women, sometimes develop rosacea: red inflamed skin, with swelling, roughness and fine, visible blood vessels, usually in the central zone of the face. Severe cases can resemble acne, irritate the eyes and lead to the bulbous red nose seen in caricatures of the elderly.

The disease affects all races but is known as the “curse of the Celts” as it is thought to especially affect people with very fair skin, although it may simply be more visible on their skin. Rosacea is commonly blamed on another alleged Celtic curse – excessive drinking. But while alcohol can trigger a flare-up, so can many other kinds of stress. Teetotallers are just as susceptible, according to the US National Rosacea Society.

Kevin Kavanagh of the National University of Ireland, in Maynooth, now thinks he has discovered the cause – and it isn’t for the faint-hearted.

Tiny mites – eight-legged arachnids related to spiders – live in the pores of our facial skin. They are particularly fond of the hair follicles of eyebrows and eyelashes, and the oily pores most common on the nose, forehead and cheeks. Called Demodex, the mites eat sebum, or facial oil, and colonise your face at puberty.

Preference for stressed skin

They crawl about your face in the dark to mate, then crawl back into pores to lay their eggs and die. Healthy adults have around one or two mites per square centimetre of facial skin. People with rosacea, however, can have 10 times as many, says Kavanagh. Research suggests that the stress that causes flare-ups of rosacea changes the chemicals in sebum, making it better food for mites.

Rosacea often improves with antibacterial drugs that don’t affect the mites, such as tetracyclines. Kavanagh thinks this is because rosacea is caused by a reaction to bacteria in the mite’s faeces.

Demodex does not have an anus and therefore cannot get rid of its faeces. “Their abdomen just gets bigger and bigger, and when they die and decompose they release their faeces all at once in the pore,” says Kavanagh. When the mites are numerous, he believes that the material is enough to trigger an immune reaction, inflammation and tissue damage.

Kavanagh notes that one kind of bacteria in the mites’ guts, Bacillus oleronius, is killed by the antibiotics that work against rosacea, and not by other types of antibiotics. His lab reported in June that 80 per cent of people with the most common kind of rosacea have immune cells in their blood that react strongly to two proteins from B. Oleronius, releasing triggers of inflammation. Only 40 per cent of people without rosacea have this reaction.

Kavanagh is now trying to get funding to develop antibodies to the bacterial proteins, to track their location and link them more firmly to the disease. Ultimately, treatments aimed at the trigger proteins may prevent rosacea.

Reference: Journal of Medical Microbiology, DOI: 10.1099/jmm.0.048090-0