Rosacea causes flushing, redness, and bumps across the nose, cheeks, chin, and forehead. It usually strikes after age 30 and affects more women than men. It tends to flare in response to certain triggers, like sun exposure or emotional stress.
“Previously, people had no real idea what caused the condition,” says researcher Kevin Kavanagh, PhD, a biologist at the National University of Ireland, Maynooth in Kildare, Ireland.
Antibiotics can help clear a rosacea flare-up. And doctors once thought that was because of the drugs’ calming effect on underlying inflammation. But puzzlingly, other drugs that target inflammation, like corticosteroids, don’t seem to help.
So Kavanagh and his team started searching for bacteria that might trigger rosacea.
How Mites Might Cause Rosacea
“We found these bacteria inside these little Demodex mites,” Kavanagh says.
Demodex mites live on the skin of 20% to 80% of adults. The tiny bugs are invisible to the naked eye. Until recently, it was thought that the mites lived harmlessly, feeding off the oily sebum that coats the skin.
Kavanagh says changes in the skin brought on by age, stress, or illness sometimes allows the population of Demodex mites to swell. Research shows that people with rosacea have more than 10 times as many Demodex mites on their skin as people without the condition.
“When each of those [mites] dies, they release bacteria into the skin,” he says.
Those bacteria trigger an immune reaction that causes redness and inflammation of the skin. The mites themselves don’t seem to be harmful, Kavanagh says. It’s the bacteria they have inside their bodies.
“You can think of them like a bus,” he says. “They bus in large numbers of bacteria. But it’s not the bus that’s the problem; it’s the bacteria that get off the bus that’s the problem.”
Kavanagh sums up the research linking Demodex mites to rosacea in a new review published in the Journal of Medical Microbiology.
More Research Needed
Right now, the idea that mites may cause at least some cases of rosacea is still just a theory. But experts who were not involved in the research say there's convincing evidence to back it up.
"It's not far-fetched at all," says Michele Green, MD, a dermatologist at Lenox Hill Hospital in New York City. "It makes perfect sense to me."
Green says the mite theory fits many features of the disease. She says many people with rosacea notice that their skin gets worse after exposure to heat and humidity, conditions that also help mites thrive.
Pharmaceutical companies also think there's something to the idea. Galderma, the company that makes Metrogel, a topical antibiotic often prescribed to treat rosacea, is reportedly testing a product that targets Demodex mites.
"There may be some cutting-edge technologies that come out of this that may work extremely well," Green says. "They may be a lot safer and better than just taking oral antibiotics."
Other experts agree that the evidence is compelling, but say it's too early to tell whether Demodex mites are a cause or a consequence of rosacea.
"This study contains evidence, but it's not proof," says John E. Wolf Jr., MD, professor and chairman of the department of dermatology at the Baylor College of Medicine in Houston, Texas.
"This theory is not a fringe theory," Wolf says. "Almost everybody with a serious interest in rosacea feels that it's a serious possibility and a serious question that deserves attention. More studies should be done to try to definitively answer the question."