A sudden purple patch on the face is associated with allergic reactions, trauma, and so on. The specific cause of the disease is recommended to go to the hospital for examination and active treatment. 1. Allergic reaction: when people use cosmetics, due to some kind of substance caused by skin allergy, it will suddenly occur on the face of purple, peeling and other uncomfortable symptoms. It is recommended to go to the hospital to check their allergens, avoid touching the allergic substances or undergo desensitization treatment. 2. External trauma: When the face is damaged by external force, blood vessels rupture and bleed, resulting in subcutaneous bruising, bruising will appear on the surface of the uncomfortable symptoms. As there are many causes of skin bruising, it is necessary to consult a doctor for diagnosis and treatment, and should not be ignored, so as not to aggravate the condition.