Diaper rash is characterized by a pair of symmetrical rashes that run the length of the fattest part of the buttock where the buttocks are in continuous and direct contact with the diaper. However, if it is complicated by bacteria or fungus, it can spread beyond these surfaces. Pustules are also common. It usually does not affect the anus. A differential diagnosis should exclude seborrhoeic dermatitis, which is characterized by oily yellowish scales, and eczema, which is accompanied by an itch. These require different treatment.