What Causes Rashes?

A woman scratches at a rash on her back.
(Image credit: ampyang | Shutterstock)

"The Healthy Geezer" answers questions about health and aging in his weekly column.

Question: What causes rashes?

Answer: The most common cause of a rash is contact dermatitis, an inflammation of the skin that comes from direct contact with irritants or allergens. A red, itchy rash from contact dermatitis isn't contagious, and usually goes away in two to four weeks.

The cause of contact dermatitis is direct contact with irritants or allergens. These include: detergents, soaps, makeup, deodorant, clothing, chemicals, rubber, metals, jewelry, fragrances, plants and medicinal lotions.

There are two types of contact dermatitis.

Irritant contact dermatitis is caused by a substance such as bleach that irritates the skin. Allergic contact dermatitis is caused by a reaction to an allergen, which is a substance that induces an allergy.

If the cause of a rash isn't obvious, you may have to get a "patch test." During one of these tests, small amounts of possible allergens are place on patches that are attached to your skin for two days. If you are allergic to a tested substance, a bump will appear on your skin.

You should seek medical attention for a rash when it interferes with your sleep or your normal daytime activities, you are in pain, you think you have an infection, or home care hasn't worked.

If you scratch a rash for a long time, you can get neurodermatitis, a condition in which skin becomes thick. Persistent scratching can also lead to infection, scars or color changes in your skin.

To treat contact dermatitis you should:

  • Avoid the irritants.
  • Use topical creams containing hydrocortisone, and oral corticosteroids and antihistamines to reduce the inflammation and itching.
  • Stop scratching.
  • Apply cool, wet compresses.
  • Cover the affected area with bandages to protect the skin and prevent scratching.
  • Bathe in cool water with baking soda or finely ground oatmeal.
  • Wear smooth-textured cotton clothing to avoid irritation.
  • Wash with mild soaps without dyes or perfumes, and rinse thoroughly.
  • Use plastic gloves to avoid contact with household cleaners.
  • When laundering, use a mild, unscented detergent and an extra rinse cycle.

The following are some common allergens:

  • Skin products. Perfumes, lotions, and cosmetics may cause allergic contact dermatitis. Others are sensitive to the preservative chemicals needed to prevent skin care products from spoiling.
  • Poison plants. These include poison ivy, poison oak, and poison sumac.
  • Rubber. Chemical additives in rubber can cause a reaction. Rubber gloves can cause dermatitis. Synthetic gloves can be used instead. Women with a rubber allergy can wear undergarments with spandex if they do not have rubber-backed fasteners or edges. Bras without rubber are also available.
  • Hair dyes. Some people are sensitive to paraphenylene-diamine (PPD). This ingredient is found in permanent hair dyes that are mixed with another chemical, such as peroxide, before application. Most people allergic to PPD can use temporary dyes.
  • Nickel. Nickel is found in gold jewelry and metal alloys. Many chrome-plated objects contain enough nickel to produce a reaction in sensitive people. Buckles, zippers, buttons and can cause dermatitis.
  • Chromates. Chromates contain chromium, and are commonly responsible for allergic contact dermatitis from cement, leather, some matches, paints, and anti-rust products. Chromates are also used to tan leather for shoes and can result in shoe dermatitis. Vegetable-tanned footwear can be used as an alternative.

If you would like to read more columns, you can order a copy of "How to be a Healthy Geezer" at www.healthygeezer.com.

All rights reserved © 2012 by Fred Cicetti

Fred Cicetti is a contributing writer for Live Science who specializes in health. He has been writing professionally since 1963. Before he began freelancing, he was a reporter, rewriteman and columnist for three daily newspapers in New Jersey: The Newark News, Newark Star-Ledger and Morristown Record. He has written two published novels:" Saltwater Taffy—A Summer at the Jersey Shore," and "Local Angles—Big News in Small Towns."