Microscopic bugs known as Demodex mites live in human eyelashes and hair follicles. These tiny creatures are arachnids, related to spiders and ticks, and colonize the skin of nearly all adult humans. For most people, the presence of these mites is harmless, existing in a balanced relationship with the host. However, when their population grows too large, they can cause significant irritation and eye discomfort.
The Biology of Eyelash Mites (Demodex)
Two distinct species of the Demodex genus colonize the human face, primarily around the eyes and nose. Demodex folliculorum is typically found in the hair follicle itself, often with multiple mites occupying a single lash. Demodex brevis burrows deeper into the sebaceous glands and the specialized Meibomian glands of the eyelid.
These mites are minuscule, measuring 0.15 to 0.4 millimeters in length, making them invisible to the naked eye. They have a semi-transparent, elongated body with eight short legs that allow them to move. D. folliculorum feeds primarily on dead skin cells, while D. brevis consumes the oily secretions, or sebum, produced by the glands.
The life cycle of Demodex is brief, lasting approximately 14 to 18 days from egg to adult. Mating occurs near the opening of the hair follicle, and the female retreats to lay eggs inside the follicle or gland. The mites are nocturnal, preferring to move and mate at night, spending their days anchored deep within the follicle.
Demodex mites are extremely common; studies suggest almost 100% of the elderly population harbors them, with high prevalence rates in younger adults. Their presence is generally considered a normal part of the skin’s micro-fauna, not an infection, until their numbers become excessive. The mites are transferred through direct skin contact, often between family members.
When Mites Cause Problems
When the mite population density becomes too high, it leads to demodicosis, which commonly manifests as blepharitis, or eyelid inflammation. The mites cause irritation through physical blockage and the release of metabolic waste products. The accumulation of these waste materials, eggs, and mite bodies can trigger an inflammatory response in the eyelid tissue.
D. folliculorum infestation is linked to cylindrical dandruff or “collarettes.” These are tiny, waxy, tube-like sheaths that form around the base of the eyelashes, composed of epithelial cells, keratin, and mite debris. This physical blockage of the hair follicle can lead to chronic inflammation, redness, itching, and a gritty foreign body sensation.
The deeper-burrowing D. brevis is associated with Meibomian Gland Dysfunction (MGD), a leading cause of evaporative dry eye. By clogging the Meibomian glands, the mites interfere with the quality of the meibum, the oil that forms the outermost layer of the tear film. This disruption causes tears to evaporate too quickly, resulting in dry eye symptoms like burning, watering, and discomfort.
In chronic cases, the inflammation and follicular distention caused by the mites can lead to structural changes in the eyelid margin. This damage may result in lid thickening, misdirected eyelashes, or the abnormal loss of eyelashes (madarosis). Symptoms only arise when the normal balance is disrupted, often in individuals with underlying skin conditions like rosacea or a compromised immune system.
Addressing an Infestation
Diagnosis of an excessive Demodex population is typically performed by an eye care professional using a slit lamp microscope. The doctor can often visually identify the cylindrical dandruff or even the mites themselves moving on the lash line. For a definitive count, a lash may be epilated and examined under a high-powered microscope. A density greater than five mites per lash is often considered pathological.
The primary strategy for managing an infestation involves consistent daily eyelid hygiene to reduce the mite population to an asymptomatic level. This involves using specialized eyelid cleansers or wipes designed to remove debris and oils from the lash line. It is also recommended to temporarily avoid oil-based facial cleansers and makeup, as these products may provide food for the mites.
For over-the-counter management, products containing Tea Tree Oil (TTO) are recommended due to their anti-parasitic properties. The active component, terpinen-4-ol, is effective at killing the mites. However, high concentrations can irritate the eye, so commercially prepared lid scrubs usually contain lower, safer concentrations, typically ranging from 5% to 15%.
In persistent cases, a doctor may prescribe pharmaceutical treatments with acaricidal effects. Topical treatments often include ivermectin cream or ointment, which paralyzes the mites’ nervous system. Widespread skin involvement may necessitate a course of oral medication, such as ivermectin, often combined with metronidazole to enhance the anti-inflammatory and mite-killing effects.