Leukoplakia is a precancerous sore (lesion) that develops on the tongue or the inside of the cheek in response to chronic irritation. Occasionally, leukoplakia patches develop on the external female genitals.

Leukoplakia mainly affects the mucus membranes of the mouth. It is caused by irritation. Sores usually develop on the tongue, but they may also appear on the insides of the cheek.

Irritation in the mouth may be caused by rough teeth or rough places on dentures, fillings, and crowns. It may also result from smoking or other tobacco use (smoker's keratosis). Persons who smoke pipes are at high risk for developing this condition, as are those who hold chewing tobacco or snuff in their mouth for a long period of time.

Leukoplakia patches may develop on the external female genital area, but the cause is unknown.

Leukoplakia may become cancerous.

The disorder is most common in elderly persons.

"Hairy" leukoplakia of the mouth is an unusual form of leukoplakia that is seen mostly in HIV-positive people. It may be one of the first signs of HIV infection. It can also appear in other people whose immune system is not working well, such as after a bone marrow transplant. It is caused by the Epstein-Barr virus, but is not harmful by itself.

White patches usually appear on the tongue and sometimes on other places in the mouth. The condition may look like thrush, a type of Candida infection that is also linked to HIV and AIDS in adults.