Ingredient review

Tris(N-Hydroxyethyl) Hexahydrotriazine

INCI: TRIS(N-HYDROXYETHYL) HEXAHYDROTRIAZINE

An effective preservative that works by releasing tiny amounts of formaldehyde, making it a controversial choice for sensitive skin.

beautyskincarepreservative

In plain English

This ingredient is a preservative that helps keep your skincare products from growing mold, bacteria, or yeast. It works by slowly releasing a very small amount of formaldehyde over time. Formaldehyde is a well-known preservative, but it can be irritating for some people, especially those with sensitive skin or allergies. Because of this, many brands now avoid it in favor of gentler options.

Review score

Safety, usefulness, and evidence

3.5Good
3.5/ 5

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
How reviews are scored

Quick decision guide

Useful, but context matters

Tris(N-Hydroxyethyl) Hexahydrotriazine 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.

  1. Step 1Start with the score, then check the irritation and clogging risk before judging Tris(N-Hydroxyethyl) Hexahydrotriazine.
  2. Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
  3. 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

moderate

Can bother some users, especially with frequent use, damaged skin, or strong companion ingredients.

Clogging risk

low

Less likely to feel heavy or contribute to clogged pores for most skin types.

Evidence level

moderate

There is useful support, but formula details and claim strength still matter.

What it is

A synthetic organic compound belonging to the formaldehyde-releasing preservative family. It is a white crystalline powder that dissolves in water and is added to cosmetics to extend shelf life.

How it works

In the product, the molecule slowly breaks down to release trace amounts of formaldehyde, which kills or stops the growth of microorganisms like bacteria and fungi. This keeps the product safe to use over time.

Pros

Effective preservation

At low concentrations, it reliably prevents microbial contamination, helping products stay safe for months or years.

Cost-efficient

It is inexpensive for manufacturers, which can keep product prices lower compared to using more expensive natural preservative systems.

Cons and cautions

Formaldehyde release

Even though the amount released is tiny, it can still trigger irritation or allergic contact dermatitis in sensitive individuals.

Growing consumer avoidance

Many people now actively avoid formaldehyde-releasing preservatives, so products containing it may be less appealing.

Best for

  • People with normal or oily skin who want a well-preserved product with a long shelf life
  • Those who do not have a known sensitivity to formaldehyde or formaldehyde-releasing preservatives

Use caution if

  • Individuals with sensitive, reactive, or eczema-prone skin
  • Anyone with a known allergy to formaldehyde or formaldehyde-releasing ingredients

Usage tips

If you have sensitive skin, check the full ingredient list for other formaldehyde-releasing preservatives like DMDM Hydantoin or Imidazolidinyl Urea.
Store products containing this ingredient in a cool, dry place to minimize unnecessary breakdown and formaldehyde release.

Safety summary

Generally safe for most people at low concentrations, but the formaldehyde release makes it a moderate irritant risk. It is best avoided by those with sensitive skin or known formaldehyde allergies.

Research notes

Studies confirm its antimicrobial efficacy and show that formaldehyde release is dose-dependent. Allergic reactions are documented but relatively rare in the general population. More recent research focuses on developing alternative preservatives with lower sensitization potential.

Common label clues

Typical concentration
0.1% to 0.5%
Regulatory status
Approved for use in cosmetics in the EU and US, with concentration limits on free formaldehyde. Always check local regulations as they may vary.
Common uses
Leave-on creams, Rinse-off cleansers, Hair care products
Environmental note
As a synthetic compound, its environmental impact is not well-studied, but it is not known to be bioaccumulative or highly toxic to aquatic life at typical use levels.

Good to know

  • The European Union allows this ingredient in cosmetics but limits the total free formaldehyde to 0.2% in leave-on products and 0.5% in rinse-off products.
  • It is sometimes listed under the INCI name 'Tris(N-Hydroxyethyl) Hexahydrotriazine' and may appear in formulas as 'THT'.

Common questions

What is Tris(N-Hydroxyethyl) Hexahydrotriazine in beauty products?

This ingredient is a preservative that helps keep your skincare products from growing mold, bacteria, or yeast. It works by slowly releasing a very small amount of formaldehyde over time. Formaldehyde is a well-known preservative, but it can be irritating for some people, especially those with sensitive skin or allergies. Because of this, many brands now avoid it in favor of gentler options.

What does Tris(N-Hydroxyethyl) Hexahydrotriazine do in a beauty product?

In the product, the molecule slowly breaks down to release trace amounts of formaldehyde, which kills or stops the growth of microorganisms like bacteria and fungi. This keeps the product safe to use over time.

Is Tris(N-Hydroxyethyl) Hexahydrotriazine safe for most people?

Generally safe for most people at low concentrations, but the formaldehyde release makes it a moderate irritant risk. It is best avoided by those with sensitive skin or known formaldehyde allergies.

Who should be careful with Tris(N-Hydroxyethyl) Hexahydrotriazine?

Individuals with sensitive, reactive, or eczema-prone skin Anyone with a known allergy to formaldehyde or formaldehyde-releasing ingredients

Research sources

Cosmetic Ingredient Review (CIR) - Formaldehyde-Releasing PreservativesOpenEuropean Chemicals Agency (ECHA) - Tris(N-Hydroxyethyl) HexahydrotriazineOpenPubMed - Contact allergy to formaldehyde-releasing preservativesOpen

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.