There are many types of skin rashes. A rash is an outbreak of many red bumps or patches on the skin. Many conditions can cause an itchy rash. In adults, several types of skin inflammation, various allergic reactions (contact dermatitis), and sometimes infection with a mite can cause a longstanding itchy skin rash.
Determining whether the condition is chronic, generally lasting more than 1-2 weeks, or recurrent, coming and going several times over weeks to months, helps to narrow the number of possible causes for the rash. The location and the extent of the skin rash on the body can also help determine a cause. Limited areas of involvement are typical of irritant or allergic contact dermatitis, as well as a form of skin inflammation called lichen simplex chronicus. A rash in body folds is often due to intertrigo or fungal infection. Eczema (atopic dermatitis), dry skin (xerosis), and psoriasis may involve either limited or extensive areas of skin covering the entire body.
Infections of the scalp include bacterial infection of hair follicles (folliculitis), infestation of head lice (pediculosis capitis), and fungal infection of scalp ringworm (tinea capitis). Itching and excessive flaking of the scalp are seen with both dandruff (seborrheic dermatitis) and psoriasis.