Urea
Also known as Carbamide, Urea, Carbonyl diamine, Carbonic acid diamide
“CIR Expert Panel says: safe as used in cosmetics.”
Urea (carbamide; CAS 57-13-6; CH4N2O) is a small-molecule nitrogen compound that occurs endogenously in skin as a component of the natural moisturizing factor (NMF). Its cosmetic safety was comprehensively assessed by the CIR Expert Panel in 2005 (IJT 24(S3):1-56, PMID 16422263), which concluded it is safe as used in cosmetic products across concentrations of 0.01–10%; the panel noted no in vivo genotoxic activity despite in vitro DNA-uncoiling observations, and flagged that urea can increase percutaneous absorption of co-applied chemicals. Urea displays well-documented dose-dependent skin activity: at low concentrations (~2–5%) it functions as a humectant through its hygroscopic nature and its role as a component of the NMF (Friedman et al. 2016, PMID 27168272; Piquero-Casals et al. 2021, PMID 34596890); at medium concentrations (15–30%) it also exhibits keratolytic activity by loosening epidermal keratin and can act as a penetration enhancer for co-formulated actives (Dall'Oglio et al. 2020, PMID 33249708); at higher concentrations (~40%) it is used medically for softening and removal of thickened nails. This dose-dependent behavior is a biological property of urea, not a regulatory restriction — the CIR issued an unconditional Safe finding applicable to cosmetic use concentrations. EU CosIng was not directly verified (JS-rendered SPA); no Annex restriction was identified for urea in a search of EU cosmetics legislation.
Humectant: hygroscopic small molecule that draws and retains moisture in the stratum corneum; endogenous component of the skin's natural moisturizing factor (NMF) (Friedman et al. 2016; Piquero-Casals et al. 2021)
Keratolytic at higher concentrations (10–30%): loosens epidermal keratin, reduces hyperkeratosis, used clinically for atopic dermatitis, psoriasis, ichthyosis, and keratosis pilaris (Dall'Oglio et al. 2020)
Penetration enhancer: can improve bioavailability of co-formulated actives (e.g., antifungals) at medium concentrations (Dall'Oglio et al. 2020)
Antimicrobial and skin barrier-enhancing properties: regulates keratinocyte differentiation and antimicrobial peptide gene expression (Piquero-Casals et al. 2021)
CIR-assessed safe with no concentration ceiling for cosmetic use; over 100-year history of safe topical application (CIR 2005; Friedman et al. 2016)
- · Urea can increase the percutaneous absorption of co-applied chemicals; formulators should account for this penetration-enhancing effect (CIR 2005, PMID 16422263)
- · Burning or stinging sensations may occur, particularly in formulations applied to compromised or diseased skin, and are more frequent at high concentrations (CIR 2005; Piquero-Casals et al. 2021)
At very high concentrations (above ~30–40%), urea transitions from a cosmetic humectant to a keratolytic/medicinal agent — products at these levels may be regulated as drugs rather than cosmetics in some jurisdictions
CIR Quick Reference Table (12/2017, revised 07/2018) — Urea row: Finding=S (Safe), Citation=IJT 24(S3):1-56, 2005
“Urea | S | | IJT 24(S3):1-56, 2005”— QRT-122017revised072018.pdf, p. 137