The difference between lichen planus and oral ulcers includes disease definition, etiology, clinical symptoms, and prognosis. 1. Disease definition: lichen planus is an autoimmune inflammatory skin disease, oral ulcer is an oral mucosal disease. 2. Etiology: the causes of lichen planus may include immunity, heredity, infection, neuropsychiatric factors and so on. The causes of oral ulcers can be infections, endocrine changes, oral mucosal injuries and so on. 3. Clinical symptoms: lichen planus is characterized by purplish-red flat papules and plaques, which may be accompanied by itching. Oral ulcers are small and shallow defects or ulcers on the oral mucosa, accompanied by pain, burning sensation and other symptoms. 4. Prognosis: the treatment cycle of lichen planus is long, after active treatment, the symptoms may subside, but most of them will leave pigmentation. Mouth ulcers can be healed after a few weeks in mild cases, but in severe cases, the duration of the disease is longer, and the disease can not be cured, and there is a certain degree of recurrence. These are some of the differences between the two diseases, the specific differential diagnosis should be carried out by a specialized doctor.