At present, there are many diseases that produce erythema clinically, usually seen in different types of skin diseases, but a few patients can also appear erythema due to autoimmune diseases or other diseases, if the patient can not determine the timely medical judgment, here are a few common cases: 1, infectious skin diseases: usually viral infectious skin diseases appear erythema is more common, such as hand, foot and mouth disease, early childhood acute rash, infectious mononuclear cell The patient usually has a history of fever before the onset of the disease, and the erythema is accompanied by a generalized rash, while the rash site has a certain time sequence, but the rash itch is not obvious; 2, allergic skin diseases: patients with these diseases are usually exposed to allergens such as pollen, mites, food and other allergens before the onset of the disease, the erythema can be accompanied by significant itching, common in hives, eczema and contact dermatitis. First of all, urticaria patients are mostly allergic to food, such as seafood, eggs, etc.; secondly, in addition to erythema, eczema can also be seen as papules and scaly changes; in addition, the erythema of patients with contact dermatitis is mostly limited to the contact area and has clear borders; 3, physical skin diseases: erythema of these diseases are mostly related to sun exposure or other external friction and damaging stimuli, commonly known as solar dermatitis, usually patients are more sensitive to ultraviolet light. The erythema mostly occurs on the face, neck, back of hands and upper limbs and other easily exposed parts, which can form chronic photosensitive skin disease if not treated in time; 4, autoimmune diseases: these diseases are mostly caused by the immune reaction of the patient’s organism to its own antigens, resulting in damage to its own tissues. Patients with lupus erythematosus can have butterfly-shaped erythematous spots with clear boundaries and infiltration, accompanied by visceral damage and systemic disease manifestations; 5, other diseases: such as psoriasis and rosacea can cause patients to produce erythematous spots, the cause of which is still unknown, but usually psoriasis patients have erythematous spots with clear boundaries and different shapes and sizes, accompanied by inflammatory redness around them; while rosacea is mostly seen in the middle of the face, especially at the tip of the nose Rosacea is usually found in the middle of the face, especially at the tip of the nose and nasal flanks, and can be evident when patients eat spicy and stimulating foods, when there is a sudden change in temperature, and when they are emotionally stressed and excited.