How do you patch test a new product?
The American Academy of Dermatology says to test a new skin care product on a quarter-sized spot, twice daily for seven to 10 days. The FDA says to do the skin test before every hair dye use. A dermatologist’s patch test is a separate in-office test. Poliage flags are not a patch test.
Three different things are called a patch test. One is a home test of a new product. One is the skin test that comes with hair dye. One is a medical test in a dermatologist’s office. This page keeps them apart and reports what each source states.
Testing a new skin care product at home
The AAD says dermatologists recommend these steps.
- Apply the product to a test spot twice daily for seven to 10 days.
- Choose a quarter-sized spot where the product will not be rubbed or washed away, such as the underside of your arm or the bend of your elbow.
- Use the normal amount and thickness you would use when applying it regularly.
- For something you would usually wash off, keep it on your skin for five minutes or as long as the instructions say.
The AAD says that if you have no skin reaction, such as red, itchy or swollen skin, after seven to 10 days, you can go ahead and use the product. If you develop a reaction, it says to gently wash the product off as soon as possible and not use it again.
The AAD adds that some ingredients, such as retinol and glycolic acid, can irritate skin, particularly sensitive skin. It says this is normal and temporary. If a reaction is severe, the AAD says you may need to see a dermatologist.
The hair dye skin test
The FDA says: “Do a patch test on your skin every time before dyeing your hair.” It also says it is important to follow the instructions and do the skin test before every use.
The FDA explains why. People can develop sensitivities with repeated exposure, and formulations may change over time. So a reaction is possible even if you have dyed your hair before without a problem. The FDA says that even if you do not see a reaction to the skin test, a reaction is still possible when you dye your hair.
The FDA page says coal-tar hair dye labels carry a cautionary statement and the product comes with directions for a skin test. The page does not give the test area or the waiting time. Those come from the directions that come with the product.
The test in a dermatologist’s office
Medical patch testing is different. The AAD says a dermatologist may recommend it to find the cause of a rash. Small amounts of allergens are placed on the skin under patches.
The AAD says you leave the patches on for 48 hours and that removing, loosening or wetting them can give inaccurate results. It says you return after 48 hours, and see the dermatologist again after 4 to 7 days, because an allergic reaction can take time to develop.
DermNet NZ describes the same test. It says the patches are usually placed on the back and that the tests are read at 96 hours, because reactions usually take 48 to 96 hours to develop. It also says patch testing is largely of value in finding the cause of allergic contact dermatitis, and is not useful for irritant dermatitis.
Contact allergy basics
The NHS says contact dermatitis is a type of eczema triggered by contact with a particular substance. It says the most common cause is irritants such as soaps and detergents, solvents or regular contact with water. Allergic contact dermatitis is less common. It can be triggered by an allergic reaction to substances in certain products, such as cosmetics.
The NHS says to speak to a pharmacist if contact dermatitis is troubling you, and to see a GP for persistent, recurrent or severe symptoms. Talk to a doctor or pharmacist about any reaction that worries you.
What Poliage does and does not do
A Poliage flag says a product lists an ingredient. It does not predict a reaction, and it is not a patch test. Your avoid list marks the ingredients you have chosen to avoid. The EU fragrance allergens guide and the fragrance guide explain two groups that often appear on labels.
Poliage gives product information, not medical advice. The label on the pack comes first, and a maker can change a formula without changing the barcode.
Where this comes from
The home test steps come from an American Academy of Dermatology page on testing skin care products. The hair dye statements come from the FDA’s hair dye page. The in-office test comes from a second AAD page and from DermNet NZ. The contact dermatitis description and the advice on pharmacists and GPs come from the NHS.