Urea

Humectant found in skin’s Natural Moisturizing Factor

Significantly improves signs of dry to very dry, scaly skin

Amounts above 5% have mild to significant exfoliating properties

Higher amounts can present aesthetic and odor issues

Synthetic versions used in cosmetics

Urea is a longstanding humectant that is a component of skin’s natural moisturizing factor (NMF), a group of substances that ensure moisture balance within skin. Topical use can play an important role in helping to shore up skin’s barrier and reduce several triggers of dry skin.

Although also a component of urine, synthetic versions are used in cosmetics. In amounts between 3–5%, urea has beneficial water-binding properties proven to moisturize and soften skin. Amounts of 10% or more have mild to significant exfoliating properties proven to reduce dry, scaly skin and help prevent water loss.

Larger concentrations (such as 40%) of urea can cause sensitivity, though such large amounts can also thoroughly exfoliate skin and have also been shown to markedly reduce severe dryness and rough, thickened texture. Higher amounts of urea are sometimes combined with salicylic acid in products meant for spot use on callused feet.

Urea can enhance the absorption of other cosmetic ingredients such as retinoids. It can also impact the pH of water-based solutions, so is sometimes use to help stabilize a formula’s ideal pH range.

Note that high concentrations of urea aren’t the most aesthetically pleasing, potentially being difficult to spread and leaving a notably tacky finish, not to mention an unpleasant, ammonia-like odor. On the other hand, the odor isn’t likely to be much of an issue if you’re applying to lower extremities instead of your face or neck.

Its long history of use in dermatology and scientific reviews over the years have consistently shown urea to be safe and generally well tolerated as used in skin care.

See: Natural Moisturizing Factor (NMF)