What Is Allantoin, What Does It Do? Source and Evidence Level
Other names: 5-ureidohydantoin
Allantoin (INCI: Allantoin) is a small molecule that is the end product of purine breakdown in most mammals; it occurs naturally in the root of comfrey, while the cosmetic version is synthetic. It is very common in soothing and skin-protecting products and is well tolerated, but its evidence is weaker than assumed: in the largest clinical study, it did not outperform a cream without allantoin.
At a glance
- INCI name
- Allantoin
- Source
- Found in comfrey root; synthetic in cosmetics
- Usage level
- Up to 2% in cosmetics; 0,5-2% in the US non-prescription skin protectant list
- What it does
- Used in soothing and skin-protecting products
- Evidence
- Rat data exist; a large human study did not outperform the carrier
- Caution
- No irritation or allergy reported up to 0,5%
What's on this page?
Most mammals other than humans produce allantoin as the end product when breaking down purines. Because humans and higher primates lack the uricase enzyme that performs this step, the breakdown stops at uric acid. Although in cosmetics it appears alongside the word "soothing", it is chemically a simple molecule, and its kinship with urea is also visible in its name: 5-ureidohydantoin.
Where does allantoin come from?
Its best-known natural source is comfrey (Symphytum officinale). About 0,6-4,7% allantoin is found in its root; it has also been detected in corn silk. Labels and marketing often describe it as "plant-based", but according to the cosmetic ingredient dictionary, the allantoin in the product is synthetic. In the laboratory it can be prepared by oxidising uric acid.
This distinction has a practical consequence. Comfrey root contains pyrrolizidine alkaloids that can damage the liver, so medical products use only extracts with these substances reduced. A comfrey extract and pure allantoin are not the same thing. On the list, see them as separate entries: Symphytum Officinale Root Extract and Allantoin.
How does it behave in a formula?
Its solubility in water is limited: at 25 degrees about 0,5% dissolves, and it is stable in the pH range 4-9. This may be one reason why it appears at low concentrations in cosmetics. On labels you may also see complexes such as Allantoin Panthenol, Allantoin Ascorbate or Allantoin Glycyrrhetinic Acid. For some of these, usage and concentration data are lacking; what is said about allantoin should not be transferred directly to them.
Why is it so common in soothing care?
In a safety assessment dated 2010, it was reported to be used in 1.376 products at concentrations up to 2%. In the US it is on the non-prescription skin protectant list at 0,5-2%. This status and its known non-irritant character are among the main reasons it is frequent in soothing creams.
Its mechanism is not fully explained. It is suggested to regulate inflammation, increase fibroblast proliferation and collagen accumulation, and soften the skin by loosening protein bonds. A review of moisturisers notes that it is marketed as moisturising and keratolytic, but the studies supporting this are lacking.
What is the level of evidence?
| Data | What was done? | Result | Level of evidence |
|---|---|---|---|
| Rat wound model | 5% allantoin lotion, 14 days | Vascularisation, fibroblast proliferation and collagen accumulation increased compared with the untreated wound | Animal data |
| Rare genetic skin disease (epidermolysis bullosa), phase 2b | 48 patients, 6% cream | Wound closure at day 2: 82% with the high dose, 41% with the carrier; by day 3 the difference was not significant | Small human study |
| The same disease, phase 3 | 169 patients, 6% cream and carrier, 90 days | Wound closure time came out the same (risk ratio 1,004, P=0,985) | The strongest data; no benefit could be shown |
In a phase 3 study, the carrier cream gave better results than expected; the researchers attribute this to the cream's own benefit or to the intensive wound care during the study. Still, the picture is clear: allantoin's effect on its own in diseased skin has not been shown. Strong studies using allantoin alone on healthy but irritated skin, measuring redness and relief, are also few. Part of the soothing effect you feel in a soothing cream may come from glycerin, oil and barrier ingredients.
Who is allantoin suitable for?
On safety, it is more reassuring. Clinical tests reported no irritation or allergy up to 0,5%. In older studies, no side effects were seen in products for nappy rash either. Data for higher concentrations are scarcer. The safety assessment also notes that data on photo-interaction, reproduction and development are not separately available. So in these areas the right phrasing is not "unsafe" but "not measured".
- If a problem arises with an allantoin product on sensitive skin, the culprit may be another part of the formula; check fragrance and essential oils too.
- Trying a new product on the inner arm or elbow crease, twice a day, for 7-10 days applies here as well.
- For a new product during pregnancy and breastfeeding, consult your doctor.
- For an open wound, a weeping rash or redness that does not go away, see a doctor rather than changing the cream.
If you want to compare soothing ingredients, you can look at the panthenol and centella pages. There is no strong direct comparison showing one of the three to be superior to the others. The routine steps for sensitive skin are explained in the sensitive skin care article.
This page is for general information only and does not replace medical diagnosis or treatment. If you have an ongoing skin or scalp problem, consult a dermatologist.