How is skin allergy testing done?

How is skin allergy testing done?

Dermatologists test for contact allergies using a process known as Patch Testing. This form of allergy testing is the most accurate test for contact allergens. Testing is much like detective work, a careful history and examination is first performed by your Skin Allergy Specialist prior to the consideration of allergy testing.

Important facts

  • Patch testing is the most accurate way of diagnosing contact dermatitis
  • Contact dermatitis is a common cause of skin rashes, including hand eczema
  • Common causes for allergies include Metals such as Nickel, Cosmetics, Leather, and preservatives
  • If a positive result is found, avoidance of the allergen can improve or cure the rash

We conduct a baseline test known as the European Standard Series, consisting of dozens of commonly encountered chemicals in everyday life. This includes substances such as metals, toiletries, leather, preservatives and glues. Added to this test are specific allergens determined by your Allergy Specialist. These substances include personal products, such as perfumes, shampoos, and cosmetics. If your condition is work related, Specialists may also include testing for work related chemicals, as this may contribute to your dermatitis.

Very small amounts of chemicals are applied to the skin on the upper back. They test area is kept in place with hypoallergenic tape. Over the next few days, if an allergy is present, the tested skin will react.

Testing is conducted over 5 days. Day one (Monday) is application of the test.  Patches are removed at 48 hours (Wednesday) and read by the Dermatologist. The result is graded from 0 to 3+.

A second and final reading is performed 48 hours after the first reading (Friday). This is designed to pick up ‘delayed reactions’, and increases the overall accuracy of the test. If an allergy is found, the skin will react by showing signs of inflammation (redness, wheals, vesicles).

In summary 3 visits are needed over the working week.

It is possible that your patch tests will be negative. This can be extremely helpful as your specialist has eliminated contact allergy as a cause of your skin condition. A negative test only means that you have not reacted to the substance tested for. In some situations what you may not react to today, you may react to in the future.

Your specialist will discuss the implications of testing with you during the initial consultation.

Once an allergy is isolated, your Dermatologist will determine if it may be the culprit for your rash. Finding the source of the allergen may lead to improvement or even cure of your condition.

  • Skin reddening and itching:
    From positive test results. This usually disappears after a few days
  • Flare of eczema
    A positive patch test may be accompanied by a flare of existing or previous eczema. Treatment is straight forward.
  • Pigmentary change
    An increase or decrease in skin colour may be seen at the patch test site- upper back.
  • Infection or scarring
    These are extremely rare.
  • Persistent reaction
    Some positive test reactions, e.g. to gold, may persist for up to a month.
  • Allergy
    Very rarely, about 1 in 600 tests, you may become allergic to one of the substances applied during patch testing.

The skin allergy clinic at Westside Dermatology does not carry out testing during the periods of November thru to February. The hot, humid weather of Brisbane can make this test difficult to perform during these months. Remember that patches are left on for 48 hours. Sweating can ‘wash out’ the allergens and can affect the test results. Planning for allergy testing can certainly be conducted at any time of the year.

  • Metals including Nickel and Cobalt
    Earrings, coins, Dental Plates, Spectacles, watch straps, rings, jean studs and belt buckles
  • Chromate
    Cement, leather, bleaches, matches, tattoos
  • Formaldehyde
    Clothes,Shampoo and cosmetics, Newspaper print, deodorant,
  • Paraphenylenediamine
    Colouring in hair dyes, Clothes, Henna Tattoos
  • Ethylenediamine
    Preservative in creams, paints, rubber, antifreeze
  • Mercaptobenzothiazole
    Rubber (boots & gloves), catheters, glues
  • Thiurams
    Rubber, fungicides, hair dye, stockings, clothing dyes
  • Balsam of Peru
    Cosmetics and perfumes
  • Colophony
    Sticking plaster and Band Aids, polishing liquids, varnishes
  • Parabens
    Preservatives in cosmetics and creams including makeup and toiletries
  • Epoxy resins
    Glues, surface coatings, PVC products
  • Topical medicated creams
    Antibiotics: Neomycin, quinoline
  • Wool alcohols
    Lanolin, cosmetics, skin creams & emollients
  • Plant allergens
    Primula, Mango Sap, Grivellas, Poison Ivy, Tulip bulbs, Onion & Garlic, Ginko, Chrysanthemums