Lichen planus is an idiopathic, inflammatory skin disease of unknown etiology. Lichen planus may involve the mucous membranes of the skin, especially the oral mucosa, scalp, nails and external genitalia. When the skin is involved, it tends to occur on the inner extremities, but may also occur throughout the body. Typically, lichen planus presents as a polygonal or round, purplish-red, flat papule with clear borders and a slow disease course. The main treatment for lichen planus is currently the application of strong glucocorticoid ointment, retinoic acid ointment, and if the patient has hypertrophic lichen planus, glucocorticoids can be used for intra-dermatological injections. In addition, if the lichen planus is severe, physical treatment can be used, such as cryotherapy, which uses liquid nitrogen at -195°C to coagulate and necrosis the lichen planus, or laser and narrow-wave ultraviolet therapy.