What is a cosmetics allergy?
Cosmetics contain many ingredients to which a person can become allergic. A true cosmetics allergy differs from simple irritation: irritation directly disturbs the skin, whereas allergic contact eczema occurs when the immune system recognises an ingredient as an allergen and triggers inflammation.
Which products are most likely to cause it?
The longer an allergenic ingredient remains on the skin, the greater the opportunity for sensitisation. Reactions are therefore particularly associated with leave-on products such as moisturisers, foundation, make-up, lipstick and mascara. Rinse-off products, including soap and shampoo, can also cause allergy, but the risk is generally lower because they are removed quickly.
Frequently responsible ingredient groups include:
- fragrances;
- preservatives;
- formaldehyde and formaldehyde-releasing ingredients;
- wool alcohols;
- cocamidopropyl betaine, especially in soaps and shampoos.
What does the reaction look like?
Allergic contact eczema usually develops where the cosmetic was applied. Typical features are redness, scaling and itching; occasionally there are small blisters or weeping areas. Symptoms most often begin 24 to 48 hours after exposure, although in a minority of cases they appear within several hours. A reaction can occur only after the immune system has previously encountered and become sensitised to the allergen, so a product that was once tolerated may later cause eczema.
Diagnosis and treatment
Stop using the suspected cosmetic while the cause is being investigated. The eczema can usually be controlled promptly with an appropriate medicinal ointment, often a topical corticosteroid prescribed for the affected area. A dermatologist can perform patch testing on the back to identify the responsible ingredient; the original product may also be tested. The result can then be compared with ingredient lists on packaging so that suitable products can be selected.
When to see a doctor
See a doctor if a rash follows cosmetic use, persists after the product is stopped, becomes severe or weeps. Seek dermatology advice when the trigger is unclear or patch testing is needed.