Urea

Urea is a component of the skin’s own natural moisturising factor, the mix of water-binding compounds held inside corneocytes. Skin produces it as a byproduct of protein metabolism, and levels are measurably reduced in dry and barrier-impaired skin.

Concentration determines what it does

This is the important thing about urea, and it is unusual among skincare ingredients. Its behaviour changes with concentration rather than simply scaling.

At low concentrations, roughly up to ten percent, urea acts as a humectant. It binds water and holds it within the stratum corneum, supplementing what skin makes naturally.

At higher concentrations, around twenty percent and above, it becomes keratolytic. It disrupts hydrogen bonds in keratin, softening and breaking down thickened tissue. This is why high-strength urea appears in products for calluses, heels and thickened nails.

The same ingredient at 5% and at 40% is doing two different jobs.

In a cleanser

Well below the keratolytic threshold, so it is present as a humectant, alongside sodium PCA and trehalose. Both urea and sodium PCA are natural moisturising factor components, which is a coherent formulation choice rather than a random one.

Source

Cosmetic urea is synthetic, produced industrially from ammonia and carbon dioxide. Despite the name’s associations, it is not animal-derived.

Who should be cautious

Urea can sting on broken or actively inflamed skin, particularly at higher concentrations. It is generally well tolerated at humectant levels.