Allantoin

Allantoin occurs naturally in comfrey root and is also a product of purine metabolism in many organisms. In cosmetics it is used for its soothing and skin-conditioning properties.

How it works

Allantoin is generally described as a keratolytic and a cell-proliferant. It increases the water content of the extracellular matrix in the stratum corneum, which softens the outer layer and helps loosen the bonds between corneocytes.

It also has documented soothing activity, and appears in products aimed at irritated, sensitive or post-procedure skin.

Concentration

Like urea, though less dramatically, its behaviour shifts with concentration. At low levels it is a conditioning and soothing agent. At higher levels the keratolytic action becomes more pronounced.

In a cleanser it is present as a soothing agent, not an exfoliant.

Comfrey and safety

Comfrey extract itself contains pyrrolizidine alkaloids, which are hepatotoxic and restricted in cosmetics. Allantoin is a single isolated molecule and contains none of them.

Cosmetic allantoin is synthetic rather than plant-extracted, produced by oxidising uric acid. That removes any question about alkaloid contamination.

In formulation

Water-soluble but with limited solubility, which caps how much can be included in a formula. Stable, well tolerated, and used at fractions of a percent to around two percent.