Contact Dermatitis: Solutions to Rash Mysteries : Allergy Testing

by Food and Drug Administration (FDA)

(Page 2 of 3)

Some drugs delivered to the individual by skin patches (transdermal therapeutic systems) — such as scopolamine for motion sickness, and clonidine and nitroglycerin for treatment of cardiovascular disease — can cause either irritant or allergic dermatitis, due either to the drug itself, a patch component, or the adhesive.

In addition, people who've been contact-sensitized by certain topical drugs may develop fever, feel unwell, or have excessive thirst when they take the drug orally as a tablet or capsule, or by injection.

Even inhaling the vapor can cause problems. One example of inhalation-related dermatitis is the "baboon syndrome" (named after the red-bottomed baboon), a curious type of red, spreading rash that develops on the buttocks and upper thighs. Japanese doctors have reported a number of cases in which mercury-allergic people, previously sensitized by the use of mercurochrome on the skin, developed the syndrome after inhaling the vapor from crushed thermometers. This ailment points out the importance of never allowing mercury to touch the skin. Alexander Fisher, M.D., one of the world's leading dermatologists, advises in Current Dermatologic Therapy (ed. Stuart Maddin, M.D.) that if a thermometer breaks, a "shiny copper object, such as a penny," should be used to pick up the mercury.

Allergy Testing

If the physician suspects an allergy, patch testing may identify the responsible agent. However, to prevent the condition from worsening, these tests are not done until the inflammation has subsided.

The dermatologist uses a series of medicines, metals, preservatives, rubber compounds, and various chemicals that go by the name North American Contact Dermatitis Group Standard Patch Test Series. A small amount of the suspected allergen(s) is applied to the patient's back, covered with a nonabsorbent adhesive patch, and left on for 48 hours. (The patch is removed if itching or burning develops before that time.) If redness, some hardness, or blistering occurs, the test is considered positive, indicating probable allergy to the substance. Since some reactions do not occur until after the patches are removed, the doctor will take another look at the patch sites in 72 hours.

Other patch test series are available if the tests are negative.

Occupational Contact

Sometimes, the offending allergen can't be easily identified. But dermatologists don't like to give up.

"When the allergen is not found, you just keep looking. So many of these cases are due to occupational contact," says Shelley. "While you're looking, treatment is directed at relieving the inflammation. It's rare that you can't do something for the patient."

Industrial statistics show that contact dermatitis accounts for more than 50 percent of all occupational illness, excluding injury, and results in about a fourth of the time lost from work. About one in every thousand workers in the United States suffers from contact dermatitis, costing millions of dollars each year.

Occupational dermatitis is common among hairdressers, workers who handle animal intestines in slaughterhouses, shrimp peelers, furniture makers working with woods like teak and African mahogany, bakers in contact with cinnamon, and many others. People with hay fever and asthma or other allergies are well advised to stay away from occupations in which they would be exposed to chemicals, water and soil, because their skin is more susceptible to dermatitis. In the workplace, about 70 percent of contact dermatitis cases are irritant and 30 percent are allergic.

A Lifelong Problem

Contact dermatitis can make its appearance as early as infancy. Acute skin problems account for one-third of visits to the pediatrician, with irritant dermatitis the most frequent type in children. A baby's thin delicate skin can become irritated from urine and bowel movements, or it can become allergic to a chemical in the diaper or medicines used to treat diaper rash.

Dermatitis of the cheeks and around the mouth can occur as a result of irritation by drooling, water, juices, food, and dry air. A rash all over the body and in the folds of a baby's skin may result from contact with detergents, soaps, fabric softeners, and bleach.

Problems can continue throughout adulthood. The problem of "dishpan" hands is common in those whose hands are constantly in contact with water, soaps or detergents. Sun lovers may develop an itchy rash following too much of a good thing, especially after the first exposure in the spring or summer. Ski enthusiasts are familiar with dermatitis and chapped skin from exposure to cold, dry air.

Frictional irritant dermatitis can result from improperly fitted shoes. Handling golf clubs and tennis rackets may produce inflamed skin, blisters and calluses. Tattooing has its dangers — people who've been sensitized to mercury, chromium, cobalt, and cadmium can develop rashes and roughened skin when tattooed with the salts of these metals.

Neither do the elderly escape. Topical medications should be used with care by older people, because changes in the skin make it more susceptible to dermatitis, and it generally takes longer to clear up than in younger patients.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.