How to patch test skincare

How to test a new skincare product

1. 1Choose a spot about the size of a quarter on the underside of your arm or inside your elbow, where the product will not be accidentally washed or rubbed off. Use skin without an existing rash or recent sun exposure.
2. 2Apply the amount and thickness you would normally use. Repeat on the same spot twice daily, such as morning and evening, for seven to 10 days.
3. 3Leave a product meant to stay on the skin in place for its normal duration. For a cleanser or another product you rinse off, follow the label's contact time; if none is specified, the general home testing method uses five minutes before rinsing.
4. 4Check the area throughout the testing period. If the skin remains free of a reaction after seven to 10 days, you can start using the product.

Why not just wait 24 hours?

An allergic skin reaction can take several days to appear. Irritation can appear much sooner, sometimes within minutes. Both can cause contact dermatitis, meaning a rash caused by something touching the skin. A single application followed by a clear morning misses the point of repeated testing: reactions can develop after repeated exposure, not only the first use.3

What should you stop for?

Watch for itching, swelling, dryness, burning, stinging or blisters, as well as colour changes. A rash can look red, purple or darker than your usual skin tone. If a reaction develops, wash the product off gently and do not use it again. A cool compress or petroleum jelly can help relieve the area. See a dermatologist if the reaction is severe and these measures do not help.13

Contact a healthcare provider if a rash spreads to other areas. Difficulty breathing needs immediate emergency care: call 911.3

Does passing mean the product is safe for your face?

Normal looking and feeling skin after repeated testing makes a significant contact allergy less likely. However, an arm test can miss a reaction on thinner skin, such as the face or eyelids. Sun exposure at the test site and a different application frequency can also affect the result. Stop if a reaction develops during wider use, even after a clear home test. Home testing is for delayed skin reactions, not for checking immediate allergies or anaphylaxis, a severe allergic reaction.2

What if you have sensitive skin or use prescription medicines?

Retinol and glycolic acid can cause temporary irritation, particularly on sensitive skin; a reaction does not automatically identify an allergy. Steroid tablets, medicines that suppress the immune system, and steroid or other immune suppressing creams on the test area can affect testing. Tell the clinician arranging allergy tests what you take and apply, and follow their preparation instructions rather than changing medicines yourself.145

When do you need medical patch testing?

If itching and rashes keep returning, a dermatologist can arrange medical patch testing to identify contact allergens. Unlike testing a whole product at home, this tests selected substances under patches, usually on your back. It investigates allergic contact dermatitis, not irritation or food allergies. Patches usually stay on for 48 hours, with later checks because reactions take time to develop. Keep every follow up appointment and keep the test area dry as instructed.467

Bring the product and its ingredient packaging to the appointment, because 'the one in the nice bottle' is not an ingredient list. Bring a medication list too. Tell the clinic if you are pregnant or breastfeeding, as medical patch testing can be postponed. Testing is not perfectly accurate; further testing is sometimes needed when the cause remains unclear.567