Lichen planus is a chronic skin condition. It causes itchy, flat, scaly patches on the wrists, legs, trunk, or genitals. It can also affect the inside of the mouth and vagina. There it resembles a white spider web. It may ulcerate. Rarely, it can also become cancerous. The scalp and fingernails can also be affected. It may become wart-like in thickness. Lichen planus may continue on and off for months or years. Scratching makes this condition worse.