Humans share their bodies with numerous microscopic organisms, and one of the most common is the eyelash mite. These tiny arachnids, belonging to the genus Demodex, live within hair follicles and oil glands on the face of nearly every adult. While the idea of these organisms moving on the skin often sparks concern, most people cannot feel these mites. Understanding their biology explains why they remain unnoticed.
What Are Eyelash Mites
The mites found on human skin belong to two main species: Demodex folliculorum and Demodex brevis. D. folliculorum is longer, measuring approximately 0.3 to 0.4 millimeters, and tends to inhabit the hair follicles, particularly those of the eyelashes. The slightly smaller D. brevis resides deeper within the sebaceous glands and the meibomian glands of the eyelids. They are translucent and elongated, allowing them to fit into the narrow structures of the pilosebaceous unit.
These mites are permanent ectoparasites, living their entire lives on the host, typically around 14 to 18 days. Their primary food source consists of skin oils (sebum) and dead skin cells. The mite population increases with age, and nearly 100% of the elderly population harbors these organisms.
Why You Usually Cannot Feel Them
The primary reason these mites go undetected is their extremely small size. Their movement is incredibly slow, calculated to be only about 8 to 16 millimeters per hour, and they tend to move mostly at night. This slow, deliberate movement deep within the hair follicle does not generate enough mechanical force to trigger the superficial nerve endings in the skin.
The mites live deep inside the hair follicles and oil glands, areas structurally distinct from the skin surface where most sensory nerves are concentrated. In low numbers, the mites maintain a commensal relationship with the host, causing no inflammatory response. The immune system keeps the mite population under control, preventing them from multiplying to a number that could cause irritation or noticeable activity.
When Mite Infestation Becomes Symptomatic
A small population of mites is harmless, but when their density increases significantly, the condition is termed demodicosis, which causes noticeable symptoms. This overgrowth often occurs in people with weakened immune systems, such as those undergoing chemotherapy, or in those with skin conditions like rosacea. Symptoms arise not from feeling the mites themselves, but from the inflammation and damage caused by their overpopulation and waste products.
Specific symptoms include chronic blepharitis, which is inflammation of the eyelids, leading to a persistent burning or stinging sensation. Excessive mite activity can also cause roughness or a sandpaper-like texture on the skin and increased itching. A telltale sign of ocular demodicosis is the presence of cylindrical dandruff, or “collarettes,” which are waxy deposits found at the base of the eyelashes. This debris is a mix of mite waste, eggs, and accumulated epithelial cells, and the resulting inflammation can lead to a foreign body sensation in the eye and even lash loss.
Diagnosis and Management
If symptoms like persistent eyelid irritation, redness, or unexplained itching occur, a healthcare provider can diagnose demodicosis through specific tests. The most definitive diagnostic method involves a microscopic examination of a few removed eyelashes or a skin scraping from the affected area. A diagnosis of demodicosis is confirmed when a mite density of five or more mites per square centimeter is observed.
Management focuses on reducing the mite population and controlling the inflammation. A simple at-home regimen involves twice-daily cleansing of the face and eyelid margins with a mild cleanser or scrub to remove the oil and debris the mites consume. Avoiding thick, greasy facial products and oil-based makeup can also help to limit their food source. Medical treatments often involve the use of topical acaricides, or mite-killing agents, such as prescription creams containing ivermectin or permethrin. Newer treatments, including specific ophthalmic solutions, are available to target the mites directly in the sensitive eye area.