Preservatives in cosmetics: phenoxyethanol, MIT and formaldehyde releasers
Is phenoxyethanol safe? Why cosmetics need preservatives, methylisothiazolinone allergy, formaldehyde releasers in shampoo and preservative-free skincare.
By the Green Point editorial teamUpdated 6 min readKey takeaways
- Any product that contains water needs a preservative system to stop bacteria and mold growing in it.
- Phenoxyethanol is one of the most common preservatives and is allowed in the EU at up to 1%; allergy to it is uncommon.
- Methylisothiazolinone (MI) caused a wave of skin allergies, so the EU banned it in leave-on products.
- Formaldehyde releasers such as DMDM hydantoin are a concern for people allergic to formaldehyde.
- "Preservative-free" products trade one risk for another and usually need special packaging and a short shelf life.
On this page
Preservatives keep cosmetics free of bacteria, yeast and mold, which can cause skin and eye infections. Most, like phenoxyethanol, are safe at the concentrations allowed, though a few cause allergies in some people. Methylisothiazolinone (MI) and formaldehyde releasers are the ones to watch if you have sensitive or allergy-prone skin.
Why do cosmetics need preservatives?
Creams, lotions, shampoos and gels are mostly water, and every time you dip your fingers into a jar or leave a bottle open in a warm bathroom, microorganisms get in. Without a preservative, they can multiply quickly. Contaminated products, especially eye products, have caused serious infections.
Preservatives can also break down over time, particularly with heat or moisture. That is why storage and the time since opening matter as much as the ingredient list.
Common preservatives and their regulatory status
In the EU, only substances on an approved list can be used as preservatives, each with a maximum concentration and sometimes extra conditions. Here are the ones you'll see most often:
| Preservative | Where you'll find it | What to know |
|---|---|---|
| Phenoxyethanol | Creams, serums, makeup, baby products | Allowed up to 1% in the EU; allergy is uncommon |
| Methylisothiazolinone (MI) | Shampoos, shower gels | Strong allergen; banned in EU leave-on products, low limit in rinse-off |
| Methylchloroisothiazolinone (MCI) | Mixed with MI in rinse-off products | Also a known allergen; limited to rinse-off products in the EU |
| DMDM hydantoin, imidazolidinyl urea, diazolidinyl urea | Shampoos, body washes, some lotions | Formaldehyde releasers |
| Parabens (methyl-, ethyl-, propyl-, butylparaben) | Creams and lotions | Effective and well studied, but debated as suspected endocrine disruptors |
| Sodium benzoate, potassium sorbate | Natural-leaning formulas, rinse-off products | Milder preservatives, often combined with others |
Ingredients such as ethylhexylglycerin and caprylyl glycol are often added to boost a preservative system, which lets brands use lower amounts of classic preservatives. Parabens have their own guide: are parabens safe?
Is phenoxyethanol safe?
Phenoxyethanol is one of the most widely used preservatives in skincare. EU rules allow it at up to 1% of the finished product, and EU scientific advisers have concluded it is safe at that level, including in products for children. Allergic reactions to it are uncommon, though it can sting on broken or very sensitive skin.
Ingredient scanners, Green Point included, flag phenoxyethanol as Regulated and Preservative because it has a legal concentration limit. That is about using it within safe limits, not proof that your moisturizer is harmful.
Methylisothiazolinone allergy
In the early 2010s, dermatologists in Europe saw a sharp rise in contact allergy to methylisothiazolinone, after it became widely used in creams, wet wipes and other leave-on products. After a review by its scientific committee, the EU banned MI in leave-on cosmetics from 2017 and, from 2018, limited it to 0.0015% in rinse-off products.
MI allergy typically shows up as an itchy, red rash, often on the face, eyelids, hands or, with wet wipes, the diaper area. Once you are allergic, even small amounts can trigger it, and it can also be found in household products such as cleaners and paints. If you are allergic, avoid both methylisothiazolinone and methylchloroisothiazolinone.
Formaldehyde releasers in shampoo and body wash
Formaldehyde releasers are preservatives that slowly release small amounts of formaldehyde, which keeps microbes in check. Common ones are DMDM hydantoin, imidazolidinyl urea and diazolidinyl urea, often found in shampoos and body washes.
Formaldehyde itself is a well-known skin allergen. Releasers are permitted within limits, but EU products must now carry the warning "releases formaldehyde" when the formaldehyde released exceeds 0.001%. People with a formaldehyde allergy are usually advised to avoid releasers altogether.
Preservative-free skincare: the trade-offs
"Preservative-free" sounds gentler, but a water-based product without a working preservative system can become contaminated quickly. Products that genuinely skip preservatives usually rely on something else:
- Water-free formulas such as oils, balms and powders, where microbes struggle to grow.
- Airless pumps or single-use packaging, which keep fingers and air out.
- Multifunctional ingredients that also have antimicrobial effects, even if they are not called preservatives.
- Short shelf lives, sometimes with refrigeration.
If you react to a specific preservative, avoiding that one ingredient is often more useful than avoiding preservatives in general. Fragrance is another common cause of reactions; see our guide to fragrance allergens in cosmetics.
What does the PAO symbol mean?
The period-after-opening symbol is a small open jar with a number and "M", such as 6M or 12M. It tells you how many months the product stays good after you first open it. In the EU it is required on products that last longer than 30 months unopened. In the US, expiration dates on cosmetics aren't required by law.
To read the rest of the label, see our guide on how to read a cosmetic ingredient list.
Frequently asked questions
Are natural preservatives safer?
Not necessarily. "Natural" preservatives, such as some plant extracts and essential oils, are often weaker and can contain fragrance allergens. Some well-tolerated preservatives, like sodium benzoate and potassium sorbate, are used in natural-leaning products, but they work best in combination. What matters is that the product stays free of microbes for its whole shelf life and that you don't react to its ingredients.
How do I know if a cosmetic has gone bad?
Look for changes in smell, color or texture, separation that doesn't mix back, or mold. Throw it away if you notice any of these, if it has passed the period-after-opening time or if it starts to sting. Eye products deserve extra care: replace mascara every few months, and throw it out after an eye infection.
Can preservatives cause acne?
Preservatives are not a typical cause of acne. They can cause irritation or allergic rashes in some people, which may look like small red bumps. Breakouts are more often linked to heavy, oily formulas or to the overall product. If a new product makes your skin break out or itch, stop using it and compare its ingredient list with products you tolerate.
Sources
- Microbiological Safety and CosmeticsU.S. Food and Drug Administration
- Shelf Life and Expiration Dating of CosmeticsU.S. Food and Drug Administration
- Phenoxyethanol (Scientific Committee on Consumer Safety opinion)European Commission
- Commission Regulation (EU) 2016/1198 amending Annex V to Regulation (EC) No 1223/2009 on cosmetic productslegislation.gov.uk (EU law archive)
This guide is for general information and is not medical advice. If you have a skin, allergy or health concern, talk to a doctor, dermatologist or dietitian. Green Point scores and Skin Scan results are informational and are not a diagnosis.
