Rashes that develop into itchy pimples on the skin affect most people at one time or another, according to the Nemours Foundation. A rash, also called dermatitis, can appear in association with a fever or other symptoms that require medical attention. Many rashes disappear in time with no treatment. See a dermatologist if your rash continues unabated, appears suddenly and itches severely or if the bumps change shape.

Hives cause itchy red pimples and usually are the result of an allergic reaction to some substance. Hives can occur following contact with pollen, chemicals, soap, food or other irritants. Hives usually are accompanied by a fever and can be serious if the reaction also causes difficulty breathing, dizziness or swelling. According to Family Doctor, hives can be as small as a mosquito bite and last for only a few hours, or they can appear as large pimply splotches and last for days.

Acne is a common skin condition that usually affects adolescents and menopausal women because hormonal imbalances cause excess oil to fill the pores, which then become clogged and form a pimple. When a pimple becomes itchy, it usually means that the pore has become infected, typically due to squeezing or exposure to germs in some way. Antibiotics usually are prescribed for itchy pimples, followed up with topical creams that contain benzoyl peroxide or retinol.

Dermatitis covers a wide range of skin conditions that produce itchy pimple-like bumps on the skin. According to Merck, the pimples result from inflammation in the upper layers of the skin. Dermatitis outbreaks can result from taking certain medications or when you come in contact with an irritant. Vericose veins can cause the inflammation and pimply sores. Constant scratching and infections also can cause itchy and bumps.

Determining the cause of the itchy bumps can be difficult, according to Merck. The source of the irritation may be from a common household product. Cosmetics, clothing materials and soaps must be considered. You should pay attention to the location of the itchy pimples to find the source. For example, if you break out on your wrist, you may be allergic to an alloy in your watch or bracelet, or you may have sun sensitivity if the breakouts occur after ultraviolet ray exposure.

According to Merck, a dermatologist can conduct skin patch tests that expose your skin to a wide variety of substances to watch for allergic reactions. The patch test is limited, however, because of the wide range of possibilities. The doctor may miss the one substance that is the actual cause of your pimple outbreaks.