Ingredient review
Diazolidinyl Urea
INCI: DIAZOLIDINYL UREA
An effective preservative that can release formaldehyde, making it a potential irritant for sensitive skin.
In plain English
Diazolidinyl urea is a preservative added to many water-based beauty products to stop bacteria, yeast, and mold from growing. It works by slowly releasing tiny amounts of formaldehyde over time. While this keeps your products safe from contamination, the formaldehyde can be irritating for some people, especially those with sensitive or allergy-prone skin. It's one of several preservatives that do the same job but have different safety profiles.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Main practical flags: irritation is moderate; clogging risk is low.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- moderate
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Diazolidinyl Urea can be useful, but watch for some irritation potential.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Diazolidinyl Urea.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
moderateCan bother some users, especially with frequent use, damaged skin, or strong companion ingredients.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
Diazolidinyl urea is a synthetic, formaldehyde-releasing preservative. It is a white, odorless powder that dissolves easily in water and is commonly used in rinse-off and leave-on cosmetics.
How it works
In a cosmetic product, diazolidinyl urea slowly breaks down to release small amounts of formaldehyde. Formaldehyde is a potent antimicrobial agent that kills or stops the growth of bacteria, yeast, and fungi, thereby extending the product's shelf life and preventing spoilage.
Pros
Effective preservation
Diazolidinyl urea is a powerful broad-spectrum preservative that prevents microbial contamination in water-based formulas, keeping your products safe to use for longer.
Low cost and stable
It works at very low concentrations (0.1–0.5%) and remains stable across a wide pH range, which helps keep product prices down without sacrificing safety.
Cons and cautions
Formaldehyde release
This ingredient slowly releases formaldehyde, which can cause allergic reactions, skin irritation, and contact dermatitis in sensitive individuals, especially with long-term use.
Not for sensitive skin
If you have a history of skin allergies, eczema, or reactions to preservatives, diazolidinyl urea may trigger redness, itching, or stinging, making it a poor choice for your routine.
Best for
- People with normal to oily skin who want affordable, well-preserved products
- Those without a history of formaldehyde allergy or sensitive skin reactions
Use caution if
- Individuals with known formaldehyde allergy or contact dermatitis
- People with very sensitive, reactive, or eczema-prone skin
Usage tips
Safety summary
Diazolidinyl urea is considered safe for most people at low concentrations, but its formaldehyde-releasing nature makes it a moderate irritant and allergen. It is best avoided by those with sensitive skin or known formaldehyde allergies.
Research notes
Studies confirm that diazolidinyl urea is an effective preservative but can cause contact dermatitis in susceptible individuals. The Cosmetic Ingredient Review (CIR) panel has deemed it safe for use in cosmetics at concentrations up to 0.5%.
Common label clues
- Typical concentration
- 0.1% to 0.5%
- Regulatory status
- Approved for use in cosmetics worldwide, with maximum concentration limits (e.g., 0.5% in the EU). Products must comply with local labeling and safety regulations.
- Common uses
- Moisturizers, Shampoos, Conditioners, Body washes, Makeup removers
- Environmental note
- As a synthetic preservative, diazolidinyl urea is not biodegradable and may persist in water systems. Its environmental impact is considered low due to the small amounts used.
Good to know
- Diazolidinyl urea is often listed near the end of ingredient lists because it is used in very small amounts.
- The European Union restricts the maximum concentration of diazolidinyl urea to 0.5% in cosmetic products.
Common questions
What is Diazolidinyl Urea in beauty products?
Diazolidinyl urea is a preservative added to many water-based beauty products to stop bacteria, yeast, and mold from growing. It works by slowly releasing tiny amounts of formaldehyde over time. While this keeps your products safe from contamination, the formaldehyde can be irritating for some people, especially those with sensitive or allergy-prone skin. It's one of several preservatives that do the same job but have different safety profiles.
What does Diazolidinyl Urea do in a beauty product?
In a cosmetic product, diazolidinyl urea slowly breaks down to release small amounts of formaldehyde. Formaldehyde is a potent antimicrobial agent that kills or stops the growth of bacteria, yeast, and fungi, thereby extending the product's shelf life and preventing spoilage.
Is Diazolidinyl Urea safe for most people?
Diazolidinyl urea is considered safe for most people at low concentrations, but its formaldehyde-releasing nature makes it a moderate irritant and allergen. It is best avoided by those with sensitive skin or known formaldehyde allergies.
Who should be careful with Diazolidinyl Urea?
Individuals with known formaldehyde allergy or contact dermatitis People with very sensitive, reactive, or eczema-prone skin
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.