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The 12 Most Common Contact Allergens in Skincare

A plain-English field guide to the ingredients dermatologists see flare allergic skin most often — where they hide on labels, what they're really called, and why even "gentle" or "natural" products keep triggering reactions.

1. Fragrance mix (Fragrance / Parfum)

Also listed as:
Parfum, Fragrance, Aroma, Perfume
Where it hides:
Lotions, cleansers, sunscreens, even 'unscented' products (masking fragrance).
Why it matters:
The #1 cause of cosmetic contact dermatitis worldwide. 'Unscented' is not 'fragrance-free.'

2. Balsam of Peru (Myroxylon pereirae)

Also listed as:
Myroxylon pereirae, Peru balsam
Where it hides:
Lip balms, healing ointments, 'natural' creams, baby products.
Why it matters:
Cross-reacts with fragrance, cinnamon, vanilla, propolis. Hidden in many 'botanical' formulas.

3. Methylisothiazolinone (MI) & Methylchloroisothiazolinone (MCI)

Also listed as:
MI, MCI, Kathon CG
Where it hides:
Rinse-off products: shampoo, body wash, micellar water, wet wipes.
Why it matters:
A leading cause of eyelid and facial dermatitis. Banned in leave-on EU products but still common globally.

4. Formaldehyde and formaldehyde releasers

Also listed as:
Quaternium-15, DMDM hydantoin, Imidazolidinyl urea, Diazolidinyl urea, Bronopol
Where it hides:
Shampoos, conditioners, body lotions, nail products.
Why it matters:
Slowly release formaldehyde as a preservative. The releaser names rarely look like 'formaldehyde.'

5. Nickel sulfate

Also listed as:
Nickel
Where it hides:
Eyeshadows, mascaras, metallic pigments, mica-heavy products.
Why it matters:
The most common contact allergen overall. Trace contamination of mineral pigments is enough to flare allergic skin.

6. Cocamidopropyl betaine (CAPB)

Also listed as:
CAPB, coco betaine
Where it hides:
'Gentle' shampoos, baby washes, foaming face cleansers labeled 'sulfate-free.'
Why it matters:
Marketed as mild but a frequent trigger of facial and scalp dermatitis.

7. Para-phenylenediamine (PPD)

Also listed as:
PPD, p-Phenylenediamine, toluene-2,5-diamine
Where it hides:
Permanent hair dye, dark eyeliners, temporary 'black henna' tattoos.
Why it matters:
Severe reactions are possible. Cross-reactions with related amines and some sulfa drugs.

8. Lanolin (wool alcohols)

Also listed as:
Lanolin alcohol, Amerchol L-101
Where it hides:
Lip balms, eczema creams, nipple creams, hand creams.
Why it matters:
Often in products marketed for damaged or sensitive skin — the exact context where reactions are most obvious.

9. Propolis

Also listed as:
Bee glue, Cera alba (with propolis)
Where it hides:
'Natural' lip balms, healing salves, K-beauty serums, honey-based masks.
Why it matters:
Cross-reacts with Balsam of Peru. Common in 'clean beauty' products that read as safe.

10. Limonene, Linalool, Geraniol, Citronellol (fragrance terpenes)

Also listed as:
Limonene, Linalool, Geraniol, Citronellol, Citral, Eugenol
Where it hides:
Essential-oil based products, 'naturally scented' lotions, citrus and floral formulas.
Why it matters:
Required to be listed in the EU above a threshold. Oxidize over time and become more allergenic with age.

11. Propylene glycol

Also listed as:
PG, 1,2-propanediol
Where it hides:
Moisturizers, deodorants, hair products, topical medications.
Why it matters:
Both an allergen and an irritant. Commonly missed because it doesn't look like a 'fragrance' or 'preservative.'

12. Benzyl alcohol & benzoates

Also listed as:
Benzyl alcohol, Sodium benzoate, Benzoic acid
Where it hides:
'Clean' and preservative-free-looking products, natural deodorants, baby creams.
Why it matters:
Used as a 'natural' preservative replacement. A frequent culprit when people react to a product marketed as gentle.

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Patch is an information tool, not a substitute for a dermatologist. If you suspect a contact allergy, ask your doctor about patch testing (e.g. the TRUE Test or an expanded series).