Erythema may be caused by drug allergy, vascular disease, physical skin disease, systemic lupus erythematosus and so on. 1. Drug allergy: drug allergy may lead to erythema on the body, especially after taking certain drugs, which may cause localized allergic reaction of the skin, then erythema will appear on the patient’s body. 2. Vascular disease: this disease usually manifests itself as a characteristic reticular or dendritic distribution of erythema, which is aggravated by cold. It may be the result of local capillary dilatation and intravascular blood circulation disorders that cause the skin to appear purple reticular changes. 3. Physical dermatosis: the lesions are generalized reticular erythema in the early stage, followed by dark red or purplish red, and finally can become brown patches with reticular capillary dilatation and hyperpigmented spots. 4. Systemic lupus erythematosus (SLE): this disease is a chronic autoimmune disease, which manifests itself as butterfly-shaped distribution of erythema on the cheeks, discoidal erythema, erythema on the palms of the fingers and nails. When patients have erythema, it is recommended to go to the hospital in time for a clear diagnosis and treatment under the guidance of doctors.