Ingredients

Bronopol — a preservative that can release formaldehyde and form nitrosamines.

Also written Bronopol

The molecule that makes cinnamon smell like cinnamon — and one of the more common fragrance allergens.

Also written Cinnamaldehyde, Cinnamic Aldehyde

A formaldehyde-releasing preservative and a known cause of contact allergy.

A preservative that works by slowly releasing formaldehyde, a known sensitizer and carcinogen. Products containing releasers must carry a warning in the EU when formaldehyde levels are high.

Treemoss, a perfume base like oakmoss, and a strong allergen for the same reasons.

Also written Evernia Furfuracea (Treemoss) Extract, Treemoss Extract

Oakmoss, a classic perfume base. A strong allergen — the EU limits the compounds in it that cause most reactions.

Also written Evernia Prunastri (Oakmoss) Extract, Oakmoss Extract

A fresh, lily-like scent ingredient. A well-known allergen, limited to small amounts in the EU.

Lyral. A strong fragrance allergen banned in EU cosmetics since 2021.

Also written HICC, Lyral

A formaldehyde-releasing preservative and a known cause of contact allergy.

A spicy, carnation-like scent ingredient and a strong sensitizer, limited to small amounts in the EU.

Wool wax. An excellent moisturiser, but a known contact allergen for a small number of people.

Also written Adeps Lanae

The alcohol part of wool wax. A good moisturiser, and the part of lanolin most often behind lanolin allergy.

Also written Lanolin Alcohols, Wool Wax Alcohols

Tea tree essential oil. Some evidence against spots, but a common cause of contact allergy — especially once it's old and oxidised.

Also written Tea Tree Oil

A strong sensitizer, usually paired with MIT. Allowed only in rinse-off products in the EU.

Also written Kathon CG, MCI, Methylchloroisothiazolinone/Methylisothiazolinone

A preservative behind an epidemic of contact allergy in the 2010s. Banned in leave-on products in the EU; allowed only at low levels in rinse-off.

Also written MI, MIT

A UVB filter that stabilises others. Can cause contact allergy, and it slowly breaks down into benzophenone in the bottle.

The key ingredient in most permanent dark hair dyes and a potent allergen — patch test every time, and never use it on skin ("black henna").

Also written PPD

A formaldehyde-releasing preservative, banned in cosmetics in the EU.

A hair-dye ingredient used in place of PPD in many permanent dyes. It's a strong allergen too — many people allergic to PPD react to it. Patch test before every colouring.

Also written 2,5-Diaminotoluene, PTD