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Diazolidinyl Urea

Broad-spectrum preservative and the stronger sibling of imidazolidinyl urea. A formaldehyde releaser with consistent patch-test positivity.

What it does

Diazolidinyl urea is a formaldehyde-releasing preservative with broader antimicrobial coverage — and higher formaldehyde release — than its sibling imidazolidinyl urea. Contact-dermatitis surveillance places it among the recurring preservative allergens, and reactions cross the whole releaser class in formaldehyde-sensitized users. It appears in both leave-on and rinse-off products. Most people tolerate it without issue; avoid it if you've flagged a preservative or fragrance sensitivity.

The evidence, graded

moderateCommon sensitivity and contact-allergy triggers in skincare include fragrance (the most-cited cosmetic allergen), essential oils, denatured alcohol, and certain preservatives (methylisothiazolinone, formaldehyde-releasers). Patch test new products on the inner forearm for 48–72 hours before face-wide use.Warshaw 2020 · Dermatitis ↗

Graded per the methodology: strong · moderate · emerging · expert consensus. A weak source on a strong claim gets the weaker label.

Also known as

Germall II

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