Many rashes have a similar appearance, but may have different causes and treatments. Dermatologists are expert at distinguishing the many different types of rashes. Some of the most common rashes are described below:
Contact Dermatitis:
Contact dermatitis is a common and sometimes significantly disabling skin condition. There are two types of contact dermatitis. Allergic contact dermatitis is a rash caused by exposure to a chemical to which a person is highly reactive, or allergic. A common type of allergic contact dermatitis is the rash caused by the poison ivy plant. Irritant contact dermatitis is a rash caused by exposure to one or many substances that physically irritate or injure the skin. Housewive's hand eczema, due to repetitive contact with water, soaps and household chemicals, is a common type of irritant contact dermatitis.
People are not born with contact dermatitis, but can develop it at any age. The appearance may vary from extensive oozing and blistery eruptions, to localized thickened and scaly patches. Even occasional exposure to an offending material may produce a dermatitis that persists or worsens over time. An ever-increasing number of chemicals and substances can act as contact allergens.
Accurate determination of the source of a contact dermatitis may require signifcant investigation. A detailed history and complete skin examination may be supplemented by allergy testing. (see Patch Testing)
Shingles:
Shingles (herpes zoster) is a blistering and often painful rash that occurs in individuals who have had chicken pox earlier in life. It is caused by a reactivation of the chicken pox virus in the nerve cells, and typically affects people over the age of 50. This reactivation may be triggered by a weakened immune system, but the exact cause is unknown. The first symptom may be pain or numbness of an area of skin followed by a red, finely blistered, band-like rash on one side of the body or face. The rash generally takes 2 to 3 weeks to develop and fade, but the associated pain from the irritation of the nerves may take much longer to resolve. Early treatment with antiviral medication will shorten the duration and severity of the disease.
Tinea versicolor:
This rash is caused by a yeast that is present on everyone's skin. In some individuals the yeast grows rapidly, causing white, pink, or brown scaly patches which can extend from the lower face or neck down to the hips. The affected area will not tan until the yeast is adequately treated. The rash is more prevalent during the warmer months of the year, and often returns in subsequent years. Treatments consist of prescription lotions or pills.
Pityriasis rosea:
This red, oval, scaly rash typically occurs in people between the ages of 10 to 40. The cause is unknown. A larger patch (herald patch) often appears first, followed several days to weeks later by multiple smaller patches on the trunk, upper arms and legs. The rash runs its course in 6 to 12 weeks. Treatment is focused on controlling the associated itching. Natural sunlight may shorten the duration of the rash.
Ringworm:
The term ringworm refers to fungal infections of the skin and scalp caused by a type of skin fungus know as dermatophyte. The affected areas are often red, round, and scaly with a ring-like appearance. People, animals, or even the soil may spread the infection. Scalp ringworm is treated with oral medication because creams and lotions cannot reach the hair root to adequately treat the infection.