Imidazolidinyl Urea

What is imidazolidinyl urea?

Imidazolidinyl urea (trade name Germall 115) is a synthetic preservative used to keep water-based products free of bacteria and fungi. Like its relatives, it works as a formaldehyde releaser: it has no free formaldehyde of its own, but slowly breaks down to release small amounts that do the antimicrobial work.

It's one of the older releasers, introduced as a "gentler" alternative to using formaldehyde directly, and it's a comparatively weak donor — it releases less formaldehyde than quaternium-15. That makes it lower-risk per use, but it is so widely used, and so often left on the skin in lotions and creams, that it remains a common contact allergen overall. In the EU it's permitted up to 0.6%.

The "paraben-free" irony

Imidazolidinyl urea is a textbook example of why the "paraben-free" label can be misleading. When consumer pressure pushed brands away from parabens, many reformulated with formaldehyde releasers like Germall 115 instead. The problem: parabens are actually among the best-tolerated preservatives, with relatively low allergy rates, whereas formaldehyde releasers sensitise more people.

So a product proudly marked "paraben-free" may have swapped a low-allergy preservative for a higher-allergy one. The label tells you what's absent, not whether what's present is kinder to reactive skin.

Why it causes reactions

The released formaldehyde binds to skin proteins and can train the immune system to mount a delayed (24–72 hour) reaction. Because imidazolidinyl urea turns up in lotions, creams, shampoos, and makeup used daily, exposure accumulates — and sensitisation often appears only after long, uneventful use. Leave-on products carry more risk than rinse-off ones because the preservative stays in contact with skin for hours.

It's also closely related to diazolidinyl urea (Germall II); the two frequently cross-react, and both cross-react with formaldehyde.

How to spot and avoid it

1. Read labels for Imidazolidinyl Urea, Germall 115, or Imidurea.
2. Prioritise leave-on products — moisturisers and makeup matter more than a quick rinse-off.
3. Avoid the whole releaser group if formaldehyde-allergic — diazolidinyl urea, DMDM hydantoin, quaternium-15, sodium hydroxymethylglycinate, bronopol.
4. Look past "paraben-free" to the actual preservative — phenoxyethanol, caprylyl glycol, or sodium benzoate/potassium sorbate are non-releaser options.

When to see a dermatologist

A slow-building, recurring rash from lotions or makeup — particularly on the face or eyelids — is a good reason to patch test. Imidazolidinyl urea and formaldehyde are on standard baseline series, so testing can confirm whether you need to avoid the whole releaser family.

The bottom line

Imidazolidinyl urea is a mild, old-school formaldehyde releaser that's mostly notable for being everywhere — and for being the preservative that quietly replaced parabens in countless "paraben-free" products. If you're formaldehyde-sensitive it belongs on your avoid list, alongside its stronger sibling diazolidinyl urea.