Possible causes of skin rashes include allergic reactions, exposure to poison ivy or poison sumac, shingles and measles, according to the American Academy of Family Physicians. A ring of red, itchy skin may be caused by ringworm, a fungus that is common in children.
In many cases, the cause of a rash can be identified by examining the qualities of the rash. If a rash consists of irregular raised or flat red sores that appear after taking a medication, the AAFP states that the rash is likely caused by an allergic reaction to that medication and recommends calling your doctor promptly. A scaly, red rash that appears in a localized area of the skin after contact with jewelry, cosmetics or perfume may be contact dermatitis, a condition that results from direct contact between an allergen and the skin.
Rashes that consist of clusters of small but painful blisters that appear only on one side of the body may be caused by shingles, states the Mayo Clinic. Shingles is a condition caused by the chickenpox virus that appears only in adults who have already had chickenpox. Another infectious disease, measles, causes a raised rash on the forehead that spreads down the face and onto the trunk, according to the AAFP. Measles is most common in children and also causes sore throat and fever.