What is Patch Testing?
Patch testing is a procedure that helps in identifying whether a person is allergic to a substance or not. Many products contain chemicals that can irritate the skin when applied. Doing a patch test helps in determining whether or not a substance is causing a reaction on the skin.
According to the American Academy of Dermatology, there are 15000 substances that can cause an allergic reaction on the skin.(1) A study was conducted and it was observed that personal skin care products caused irritant contact dermatitis in 289.8% males and 39.5% of females.(2) Performing a patch test at home can help in determining which cosmetic product or ingredient is responsible for a skin reaction.
Patch testing involves applying a small amount of product to the skin and leaving it to see if any reaction develops. It is different from an allergy test that is done by an allergist to identify what substance is causing the allergy. The allergy test is usually a prick test that may lead to the sudden development of symptoms while in a skin patch test a reaction may take several days to develop.
Patch testing is also offered by a dermatologist in their office.
How is a Patch Test Performed?
Following steps should be taken when performing a patch test for a new skin care product:
- Apply a small amount of skin care product to a small patch on the skin, an area that would not be washed frequently. The best areas can be inside of the arm or bends of the elbow.
- Apply the product thickly similar to how it would be used.
- Leave the skin care product on the skin as long as it would normally be on the skin when used regularly. For example, if testing a cleanser apply it on a patch for about 5 minutes or as mentioned in the instructions.
- Repeat the test twice a day for about 7-10 days as a reaction may not show up immediately. It is therefore important to apply the product continuously.
- If a reaction is noticed the area should be washed off immediately and its usage should be stopped. A cold compress or petroleum jelly can be used to soothe the reaction.
Importance of Patch Testing
Skincare products are made of different ingredients that may irritates the skin and even cause an allergic reaction.(3) This can help in knowing whether or not a person’s skin is able to tolerate the product before using it over a larger area.
When a substance irritates a skin, it can lead to dermatitis or inflammation of the skin. This is known as contact dermatitis.(4)
Contact dermatitis can be either irritant contact dermatitis or allergic contact dermatitis. It is basically a hypersensitive reaction that can take a few hours to develop. Patch testing a product for at least 7 days before fully using it may prevent the occurrence.
What Chemicals Should a Person be Aware of While Using Any Skincare Product?
Skincare products contain various chemicals that may cause reactions. The typical irritants include:(5)
- Benzalkonium chloride
- Propane sulphone
The research found propylene glycol, an emulsifier to be commonly found in creams and lotions.(6)
Symptoms To Look Out For In An Allergic Reaction
The symptoms of the allergic reaction depend on the product, where it is applied, and how often it is used. The symptoms can be:
A study done in 2018 found that most of the reactions occurred on the face followed by the neck and the most common cause were soaps and face creams.(7)
A study done in 2019 noted that many people had reactions to cosmetics on eyelids.(8)
When to See a Doctor?
If skin irritation is observed after applying any product, the best first thing to be done is to stop the usage of the product and second is to consult a dermatologist for necessary intervention. If there is a severe reaction that is not getting better with a cold compress or petroleum jelly a doctor’s help should be taken.
A doctor can be looked out for if:
- There is bleeding and oozing of pus from a rash
- There is a skin allergy
- There is breathing difficulty
- Hives appear all over the body
- A rash is not improving even after 2-3 weeks
A doctor can guide what help should be taken and what ingredients need to be avoided.