Lichen planus causes the skin to break out in itchy, purplish bumps that spread, according to Healthline. Often the lesions blister, then scab over. Sometimes thin white lines develop over the rash. The lesions usually clear up on their own within six to 18 months.
The most common form of lichen planus affects the skin, Healthline reports. It usually starts at the wrists or inner forearms, but it can occur anywhere on the body. The lesions spread for two weeks to a few months. Although it is uncomfortable, most cases are not serious.
Less common forms of lichen planus affect the mouth, genitals, scalp and nails, Healthline states. These forms can be more serious and require treatment. Individuals with a rash on their genitals or in their mouth should seek medical treatment.
Lichen planus is triggered by an immune system response, Healthline explains. It can be caused by an allergy, stress, a viral infection or genetics. Sometimes patients with autoimmune diseases develop lichen planus as well.
Middle-aged adults are most likely to develop lichen planus, Healthline says. Women are more likely to develop the form that affects the mouth. The skin form of lichen planus affects both men and women equally.