Patch Testing Natural Ingredients: What Dermatology Sources Say

A patch test is a clinic test that finds the cause of allergic contact dermatitis, a skin allergy. It applies small amounts of suspected allergens to the skin under tape. It does not replace seeing a clinician about a rash. If you have symptoms of a severe reaction such as trouble breathing, FDA says to call 911. [1]

Two kinds of skin reaction

The NHS describes contact dermatitis as caused either by an irritant, a substance that directly damages the outer layer of skin, or by an allergen, which triggers an immune response. [2] Irritants such as soaps and detergents are the most common cause. [2] Allergy is less common and can be triggered by substances in products such as cosmetics. [2] This matters because DermNet says patch testing is largely of value for allergic contact dermatitis and is not useful for irritant dermatitis. [3]

How a clinic patch test works

• The suspected allergens are applied, diluted, usually to the back, for 48 hours. [3]
• FDA says a physician inspects the skin after 72 to 96 hours, and that patch testing requires two to three office visits. [1]
• A standard "baseline" set of allergens will pick up about 70 percent of contact dermatitis, according to DermNet. [3]
• Your own products can be tested too, and some may need to be diluted to the right strength. [3] DermNet says it helps to bring product packaging. [3]

What the sources say about "natural" ingredients

DermNet says Balsam of Peru comes from the bark of a tree it spells Myroxolon balsamum. [5] The accepted spelling in the GBIF taxonomy is Myroxylon balsamum (L.) Harms, family Fabaceae. [7]

Testing at home: what is and is not described

Some dermatology sources describe a simple home check for leave-on products, but they attach limits.

• DermNet describes "repeat open application testing" as something that can sometimes help identify a suspect item while formal patch testing is delayed. [3] It says no visible redness or swelling means contact allergy to that product is unlikely. [3]
• DermNet also says self-testing a product for Balsam of Peru should be done only after first talking with a doctor, and that the product may still cause an irritant reaction. [5]
• DermNet says shampoos, conditioners, soaps and cleansers should not be tested this way because they frequently cause irritant dermatitis. [5] It adds that some highly irritant products cannot safely be tested. [3]
• For hair dyes, FDA notes that some makers instruct users to test a small amount first. [1] Follow the product's own directions.

Allergic rashes tend to appear hours or days after contact. [8] A reaction may therefore not show straight away.

When to ask a clinician

The NHS says to see a GP for persistent, recurrent or severe contact dermatitis, so the cause can be sought. [2] For essential oils specifically, see Patch Testing and What to Do After a Skin Reaction. For the products most often involved, see Common Contact Allergens in "Natural" Products, Natural Does Not Mean Hypoallergenic and Skin and Hair Safety: When to See a Doctor. For severe reactions see Severe Allergic Reactions to Natural Products.