Urea

Urea is one of the molecules your own skin makes to hold water, part of what keeps the surface soft, and the version in skincare does the same thing: it draws in moisture, and at higher strengths it helps loosen and shed dead skin, which is why it turns up in creams for eczema, psoriasis, rough heels, and keratosis pilaris. The most common worry about urea is a case of mistaken identity. Urea is a single, stable compound that does not release formaldehyde. The ingredients people are thinking of are diazolidinyl urea and imidazolidinyl urea, which are different, larger, synthetic preservatives that share part of the name and do slowly release formaldehyde. Plain urea is not one of them, and skipping urea over that mix-up means passing on a moisturizer that earns its place. On its own merits urea is well tolerated and naturally present in the body. The one real caveat is concentration: the high-strength keratolytic versions, in the tens of percent, can sting or irritate on sensitive or cracked skin, so those are worth easing into. As a humectant at ordinary levels, it is about as gentle as moisturizers get.