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Mysterious Rashes May be Allergies That are Skin Deep

May 20, 2015

In spring, I start seeing a steady trickle of patients coming in with intensely itchy, raised, red and blistery skin rashes. I can usually confidently diagnosis a poison ivy dermatitis and give the patient relief with steroid medications. About 80% of the population is allergic to poison ivy. Poison ivy is just one example of an allergic contact dermatitis. 

There are literally thousands of potential allergens, though, in our environment that can stimulate the same type of itchy rash reaction in a sensitized patient. To be sensitized, you must have been exposed at least once to the allergen. Some patients, however, won’t develop an allergy until they have used a product for years. Specific cells of the immune system become primed to create inflammation on subsequent exposures to an allergen.

The rash of an allergic contact dermatitis is usually at the site of contact with the allergen, although severe cases may extend outside the contact area or may become generalized. The pattern often suggests the allergen. Some typical allergic contact dermatitis patterns include:

  • Red, itchy scalp after dying the hair due to the hair dye paraphenylaminediamine.
  • Rashes on both the hands and feet due to potassium chromate, a chemical used in tanning leather.
  • A rash around the navel due to an allergy to nickel found in belt buckles.
  • Itchy, red hands due to methylisothiazolinone, a preservative found in shampoos, certain soaps and baby wipes.

Other presentations may take some time to figure out. Eyelid rashes, for example, are often due to allergens that are brought to the eyes by rubbing. One patient I saw with an eyelid dermatitis actually had an allergy to gold. She would unknowingly touch her gold earrings and later rub her eyes. Strict avoidance of the allergen is mandatory.

A dermatologist can help you find out if allergen is the cause of your rash. A good history and exam is usually sufficient to suggest the culprit, but sometimes allergy testing is necessary. For me, finding the cause of someone’s unrelenting itch is one of the most rewarding aspects of dermatology.


Dr. Timothy Monahan is a dermatologist with Day Kimball Medical Group in Danielson.

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Charity McClure, FNP-C

Charity McClure, FNP-C

Internal Medicine

I grew up in Asheville, North Carolina, where I learned to love the outdoors and embrace new experiences. After completing my first undergraduate degree in biology I moved to Washington, D.C. to work...more »
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