Rashes on the limbs may be related to eczema, urticaria and psoriasis. 1. Eczema: the cause of eczema is not yet clear, may be caused by a variety of internal and external factors, such as heredity, immune abnormalities and endocrine and so on. Clinical manifestations of eczema include erythema, papules and blisters, which can be seen in all parts of the body. 2. Urticaria: This disease is clinically manifested as wind clouds (red or pale white), angioedema, etc. The lesions can develop in all parts of the body, commonly found on the trunk and proximal extremities. The causes of this disease are mostly related to food, infection, drugs and physical factors. 3. Psoriasis: The causes of this disease are related to environmental factors, immune factors and genetic factors, etc. The patient’s skin will appear red papules or maculopapular rashes, plaques, which are covered with silver-white scales, and can involve the whole body, commonly found on elbows and knees, etc. The cause of the red rash on the limbs can be found in all parts of the body. There are many causes of red rashes on the limbs, so it is recommended that the patient consult a doctor to clarify the cause of the disease.