White eyelashes are often caused by a medical condition known as vitiligo. In addition to the loss of pigment on the eyelashes, vitiligo can also cause loss of pigment on the hair on the head, and facial hair.
Vitiligo is an autoimmune disorder that generally strikes before the age of 40. It affects men and women equally, and in addition to whitening of the hair, this condition also leads to areas of patchy whiteness on the skin. Those who have existing autoimmune conditions such as hyperthyroidism as well as people with family histories of vitiligo are at a greater risk for developing it.