Eyelash mites, scientifically known as Demodex, are microscopic, eight-legged organisms that live on the skin of nearly all humans. They are a type of ectoparasite and are considered the most common permanent microscopic inhabitant of human skin. While the thought of tiny mites living in hair follicles may be unsettling, their presence is typically harmless and asymptomatic. Problems arise only when the mite population grows excessively, leading to an inflammatory condition known as demodicosis.
The Biology of Eyelash Mites (Demodex)
Two species of Demodex colonize humans: Demodex folliculorum and Demodex brevis. These mites are tiny, with D. folliculorum measuring 0.3 to 0.4 millimeters in length, and D. brevis being about half that size. Their elongated bodies are adapted for life inside the narrow structures of hair follicles and glands on the face.
D. folliculorum primarily lives in hair follicles, often near the opening, and multiple mites can inhabit a single follicle. D. brevis burrows deeper into the sebaceous glands and Meibomian glands, where it is generally found alone. The mites feed on skin cells, dead skin, and sebum, the oily substance produced by the sebaceous glands.
The life cycle of the Demodex mite lasts around 14 to 18 days. The female lays eggs inside the hair follicle or sebaceous gland, and the mites go through larval and nymph stages before maturing into adults, a process that takes about a week. Mating occurs near the opening of the hair follicle, typically at night when the mites are more active and crawl across the skin’s surface.
Prevalence and Factors Affecting Mite Population
Colonization by Demodex mites is incredibly common and increases significantly with age. While prevalence is around 12% in children, it rises sharply in adults. By the time individuals reach their 60s, the prevalence can be as high as 84%, and it is estimated to reach nearly 100% in people over 70 years old.
Simply having Demodex mites is normal and not a cause for concern in most cases. The primary factor leading to problems is not the presence of mites, but the density of the population on the skin. A high population density is more likely to trigger an inflammatory response and lead to symptoms.
Age is a significant factor in population growth, possibly because older adults have had more time to acquire the mites or due to changes in skin composition and immune function. Certain pre-existing conditions also correlate with an increased risk of mite overgrowth, including inflammatory skin disorders like rosacea and seborrheic dermatitis. Individuals with compromised immune systems or metabolic disorders like diabetes may also be more susceptible to overgrowth.
Recognizing Symptoms of Mite Overgrowth (Demodicosis)
When the mite population density becomes too high, the resulting inflammatory condition is called demodicosis, which often manifests as chronic eyelid inflammation (blepharitis). Symptoms of mite-related blepharitis include persistent itching, a burning sensation, and redness along the eyelid margins. Patients may also report a foreign body sensation or blurry vision due to an unstable tear film.
A specific sign of Demodex infestation is the presence of cylindrical dandruff, also known as collarettes, at the base of the eyelashes. This material is a waxy, tube-like accumulation of mite waste, eggs, keratin, and epithelial cells that forms a sleeve around the lash shaft. The presence of this cylindrical dandruff is a strong indicator of an active Demodex infestation, especially D. folliculorum.
The mites’ activities can also contribute to dry eye syndrome and meibomian gland dysfunction, as D. brevis lives deep inside the oil-producing glands of the eyelids. The mites mechanically irritate the follicles, and the release of their internal contents upon death can trigger an inflammatory cascade. Diagnosis is typically confirmed by an eye doctor or dermatologist who removes a few eyelashes and examines them under a microscope.
Management and Prevention Strategies
The goal of managing demodicosis is to reduce the mite population to a level that no longer causes symptoms. Management begins with diligent eyelid hygiene practices to mechanically remove mites and debris. Washing the eyelids and face daily with a gentle cleanser helps control the mite load and remove the oils and skin cells they feed on.
Tea tree oil (TTO) and its active component, terpinen-4-ol, are frequently used over-the-counter options due to their strong acaricidal properties. Products containing a diluted concentration of TTO, such as specialized eyelid wipes or cleansers, are used for daily home therapy. For severe cases, a healthcare professional may perform in-office lid scrubs using higher concentrations of TTO.
In addition to hygiene, prescription topical treatments containing antiparasitic medications like ivermectin cream may be used to reduce mite density in persistent cases. To prevent reinfestation, it is important to avoid sharing cosmetics and to wash pillowcases and bedding frequently in hot water. Patients are also advised to replace old eye makeup, as these items can harbor mites and contribute to recurrence.