I Have A Skin Rash: Is It Allergic Contact Dermatitis?

By Dr. Richard Thomas, MD, FRCPC

When you talk to a dermatologist about allergies, you may think of a condition called allergic contact dermatitis.

This occurs when a substance has come in contact with the skin and the immune system, over 1-2 weeks, mounts an immunologic response causing swelling, redness and itching. This is different from an irritant contact dermatitis, which is caused by an irritant breaking down the protective barriers of the skin. For example, it's what you'd see if you were to wash your hands with strong soap 50 times/day. Dermatitis sometimes looks like eczema, so check out the rest of this site to compare them.

How does allergic contact dermatitis look?

  • Well defined, red, swollen blisters that are ongoing during the acute stage. They form initially at the place of contact with the allergen, but may later become more widespread.
  • If the process has gone on for a long time, the skin may become thickened and scaly.

Food Allergies

Many patients think of skin allergies as those related to reactions on the skin from foods or pollen or molds. Food allergies occur most commonly in infants and children who have atopic eczema. Cows' milk, eggs, peanuts, soy and wheat are the highest risk foods. Others will react to other foods, such as shellfish, strawberries, and tomatoes. True food allergies are much more difficult to accurately test; the best way may be to abstain from eating the food for a period of time, then try the suspected food again and look out for skin changes. Hives (urticaria) may also develop in response to foods allergies.

How do you prove an allergic reaction?

  • Perform patch tests. A standard battery of known allergens are placed on the skin in small chambers and left in contact for 2-3 days. Allergic reactors will be seen as swollen red bumps. Those tests are performed by dermatologists.
  • Take the suspected product and rub it on to a spot on the inner upper forearm twice a day for 3-4 days. A reaction should be seen if an allergy is present.

What are the most common substances that we are allergic to?

Your symptoms can be an allergic reaction to the fragrances and preservatives in products including:

  • Skincare products   28 per cent
  • Haircare products   24 per cent
  • Facial cosmetics   11 per cent
  • Nail cosmetics   8 per cent
  • Fragrance products   7 per cent

Also pay attention to natural products that contain rosemary, sandalwood, arnica, chamomile, vitamin E, tea-tree, lavender oil, cinnamon alcohol, eugenol, genaniol, musk ambrette.

Other common allergy triggers include:

  • Nickel
    -   This is the most common test to be positive. It is commonly found in costume jewelry, such as earrings and necklaces, as well as buckles and snaps.
  • Balsam of Peru
    -   This is a naturally occurring fragrance found in cosmetics, and also in spices such as cloves, cinnamon.
  • Fragrances
    -   These are often found in cosmetics.
  • Thimerosal
    -   This is a preservative used to prevent bacterial growth in cosmetics.
    -   It is also used as an antiseptic in contact lens solutions.
  • Formaldehyde
    -   This substance can be found many products, such as textiles, paints, cigarette smoke, paper, plastic bottles, etc.
    -   It is rarely used in cosmetics these days.
    -   In textiles, it is used as a finish on wash and wear, wrinkle resistant, permanent press, or drip dry clothes.
  • Quaternium 15
    -   This is a preservative used to prevent bacterial and fungi from growing in personal care products.
  • Neomycin and Bacitracin
    -   These are found in commonly used OTC antibiotic creams.

If you find you have an allergy, the only way to prevent reactions to the allergens is to avoid them.

Six tips to stay comfortable

  1. If the irritated areas itch, apply cool, damp compresses.
  2. Do not scratch - it can cause scarring, infection, increased pigmentation, and thickening of the skin. Instead, gently pat the skin.
  3. Avoid hot water. Decrease the number of showers and baths you take.
  4. Avoid soaps, detergents and overheated rooms.
  5. If the irritated area is dry, use an emollient such as Aquaphor, Eucerin, Vaseline or Acid Mantle.
  6. Do not put alcohol or antiseptic lotions on your lesions.

Follow the link for information on various types of dermatitis and to compare it with eczema. For more general information about treating your skin correctly, go to SkinCareGuide.ca.


About the author:
Richard Thomas, MD, FRCPC is Clinical Assistant Professor of Clinical Dermatology, Division of Dermatology, University of British , Vancouver, Canada.


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