Eyelashes simply protect the eyes from injury. However, lush eyelashes are also considered characteristics of beauty and femininity in most societies, according to an article titled "Bimatoprost in the Treatment of Eyelash Hypotrichosis," by Simon K. Law in the April 2010 issue of the journal Clinical Ophthalmology. Humans normally have 90 to 160 eyelashes on the upper eyelid and approximately 80 on the lower. Each lash typically lasts for three to six months. There are a variety of possible causes for loss of eyelashes, and patients should be evaluated by a physician to rule out a serious underlying disorder.
Eyelash loss can result from an overactive or underactive thyroid glands, according to an article by David R. Jordan, M.D. in the February issue of the journal Seminars in Plastic Surgery. An overactive thyroid gland may be accompanied by the inability to tolerate heat, weight loss, difficulty sleeping, headaches and swelling of the lower neck. The hair breaks off, resulting in thinning and bald patches that may also occur in the eyelashes and eyebrows. An underactive thyroid gland may produce symptoms of intolerance to cold, weight gain, dry skin and constipation. Eyelashes and eyebrows may become sparse as the hair thins and becomes dry and brittle.
Sufferers of trichotillomania have powerful urges to pull out their own hair, and thus, noticeable hair loss from the head, eyebrows and/or eyelashes results. Increasing emotional tension usually precedes the hair pulling, according to an article by Samuel R. Chamberlain, M.A.,and colleagues in the April 2007 issue of the American Journal of Psychiatry. After pulling hair out, patients commonly experience gratification and stress relief. It is suggested that trichotillomania is one condition on the obsessive-compulsive spectrum, which also includes severe nail biting, eating disorders and obsessive compulsive disorder.
Alopecia areata is a disorder of the immune system that causes hair loss. Immune cells attack the hair follicles, causing the hair to fall out. Alopecia areata can cause loss of all hair on the body or loss in just one area where hair grows, such as the eyebrows, eyelashes, scalp or beard, the American Academy of Dermatology explains. Alopecia areata has an unpredictable course. Hair may only be lost once or may be lost and regrown many times, over several years. There is no cure, but treatments that promote hair growth can minimize the severity, such as topical minoxidil and corticosteroids injected into bald areas, taken orally or applied to the skin.