Last month, the popular magazine New Scientist published a story that might have had some readers’ skin crawling – or at least the tiny critters residing upon it.
The story detailed research by Kevin Kavanagh, a biologist at the National University of Ireland Maynooth, who suggests the skin condition rosacea may be caused by the feces of mites hunkered down in facial pores.
Rosacea is a common, recurring condition (more than 14 million Americans are affected) that is characterized by inflamed skin, including swelling, roughness and visible blood vessels. Rosacea is typically found on the face, and sometimes called “adult acne.” Severe cases can cause eye irritation and result in a red, bulbous nose that, erroneously, has caused rosacea to be associated with alcohol consumption. The latter may trigger the condition; it does not cause it.
In fact, the cause(s) of rosacea is poorly understood. Kavanagh’s hypothesis singles out Demodex mites – tiny parasitic arachnids that live in or near hair follicles (most notably eyebrows and eyelashes) on mammals, including humans, where they feed on sebum, an oily secretion that lubricates and waterproofs skin and hair.
Healthy adults, according to Kavanagh, have one or two mites per square centimeter of facial skin; persons with rosacea may have 10 times that number. The mites lack anuses and simply store waste material inside them. When they die and decompose, the accumulated fecal matter is released, prompting a strong immune response that results in inflammation and tissue damage.
Antibacterial drugs don’t affect the mites. Stress, which appears to exacerbate rosacea, alters chemicals in sebum, making it better food for the mites, according to the New Scientist article.
Of course, the whole story is much more complicated. In research published in 2007, a team of scientists led by Richard Gallo, MD, PhD, professor of medicine and chief of the Division of Dermatology at the UC San Diego School of Medicine and the Dermatology section of the Veterans Affairs San Diego Healthcare System, described two underlying abnormalities they linked to the emergence of rosacea.
First, they said, patients with rosacea appear to have far more anti-microbial peptides – small proteins that are part of the body’s host defense system – than normal. These peptides caused the exact same symptoms in the skin that rosacea does. They also react to the same environmental triggers, such as spicy foods, heat, alcohol and stress.
The overabundance of peptides was linked to an overabundance of their precursor, a molecule called cathelicidin that is normally associated with protecting the skin from infection. In other skin diseases, a deficiency of cathelicidin correlates with increased infection. In rosacea patients, researchers found the opposite was true; too much cathelicidin was present in their skin. They also observed that it was a different form than found in people without the skin disorder.
Second, patients with rosacea also had greatly elevated levels of enzymes called stratum corneum tryptic enzymes (SCTE). These enzymes turned the precursor into the disease-causing peptide. When Gallo and colleagues injected mice with the cathelicidin peptides found in rosacea, or added SCTE, they increased inflammation in the mouse skin, thus proving that these abnormalities can cause the disease.
Given his expertise on the subject, we asked Gallo what he thought about the mite-rosacea connection:
Q: How plausible is the mite hypothesis as a cause of rosacea?
A: It’s been around for many years. There have been previous studies by Frank Powell in Ireland, though follow-up research has shown that mites are not usually associated with rosacea. Still, our findings suggest it is entirely possible that in some patients an increase in skin mites could serve as the trigger.
Q: Your work posits that rosacea results from a more fundamental problem: the abnormal functioning of the innate immune system. What do you mean?
A: The fundamental problem in rosacea is genetically encoded increased susceptibility to the environment. The innate immune system is this genetic system. Because of this abnormality, a variety of outside factors, from sunlight to bacteria to mites, could all set it off.
Q: What does all of this mean in terms of finding new or more effective treatments for rosacea?
A: More effective treatments would normalize skin sensitivity by inhibiting the genes that are hyperactive. That’s part of what we’re looking at now.