Allergy Patch Testing

What Can Allergy Patch Tests Test For?

Allergy patch tests are a reliable method for identifying triggers of delayed allergic reactions, particularly contact dermatitis. Unlike immediate allergies that cause symptoms like hives or sneezing, these tests target substances that irritate your skin hours or days after exposure. The results can help pinpoint specific allergens and guide you in avoiding them.

1. Metals

Metals are a common cause of allergic skin reactions.

• Nickel - Widely present in jewelry, buttons, zippers, and eyeglass frames.
• Chromium - Found in leather goods and construction materials such as cement.
• Cobalt - Often used in metal alloys and some pigments in paints or cosmetics.

2. Preservatives

Preservatives in everyday items can lead to unexpected skin reactions.

• Formaldehyde - Used in cleaning products, textiles, and some cosmetics.
• Methylisothiazolinone (MI) - Found in shampoos, liquid soaps, and wet wipes.
• Parabens - Common in personal care products like lotions and makeup.

3. Fragrances

Fragrance allergies are widespread, as scents are added to everything from perfumes to cleaning products. Patch tests can check for sensitivity to specific fragrance mixes or individual scent components.

4. Rubber and Latex Chemicals

These substances are often found in everyday items but can irritate sensitive skin.

• Natural rubber or latex - Present in gloves, balloons, and elastic bands.
• Thiuram and carbamates - These are used in the production of rubber-based materials, including some shoes.

5. Hair and Skin Care Ingredients

Products meant for beauty or hygiene are frequent culprits.

6. Dyes and Pigments

Dyes used in clothing or tattoos can be allergenic.

• Textile dyes - Can cause irritation, especially in tightly worn fabrics.
• Tattoo inks - Reactions are most common with red and black pigments.

7. Medications and Topical Treatments

Certain medications applied to the skin can trigger allergies.

• Topical antibiotics - Neomycin and bacitracin are two common irritants.
• Corticosteroids - Ironically, these creams used to treat skin issues can sometimes cause reactions.

Allergens in small metal discs are put on your back and taped in place. It’s a commitment, as you’ll have to leave them on for at least 72 hours. You return to the clinic after 2 days and 3 or 4 days, to have any reaction inspected. Some reactions come on quite quickly, others appear later.

You can’t shower or go swimming while the units are taped to your back, which is worth bearing in mind for planning.

It’s important to ensure that you have no eczema or dermatitis on your back at the time of testing, otherwise results are difficult to interpret. Your specialist can treat this as needed before testing starts.

Such a small amount of potential allergen is used in the testing process that the risk is very low. The reaction is usually mild and confined to a small area, but there’s a possibility you have a bigger reaction, especially if you test positive to multiple substances.

There’s a medical adage that goes, if you test for something, you should be ready for the answer. Tests don’t always confirm what you think – a substance you believe is definitely causing your rash may not actually give a positive result. And something you thought you were fine with may actually prove reactive in testing. How do you interpret this? That’s for your specialist to discuss with you, but generally, your own experience usually trumps allergy testing results.

There are private clinics that offer patch testing – dermatologists or allergists are the medical specialists for this area of expertise, and it does require skill to test for the right things and interpret results. They can determine an irritation from a true allergy, and advise on the best action plan. Other non-doctor private clinics offer patch testing and other types of allergy testing.

Your GP may consider referring you for patch testing or to a dermatologist in certain circumstances. This is if your eczema has suddenly got worse, or if you have hand, face or genital skin rashes that are recurrent or resistant to standard treatment. There's often a bit of a wait for this on the NHS.

Your GP may refer you for work-related dermatitis, but if your employer has private cover or access to an occupational medicine doctor, this may be a good place to start and will be much quicker. And any action plan can be implemented directly in the workplace.