Quick Comparison
| Ceramides | Urea | |
|---|---|---|
| Typical Concentration | Look for products containing ceramide NP (ceramide 3), ceramide AP (ceramide 6-II), and ceramide EOP (ceramide 1) — these are the most abundant in human skin. Often combined with cholesterol and fatty acids in the optimal 3:1:1 ratio. Apply as moisturizer morning and night. | Moisturizing: 2-10%. Mild exfoliation: 10-20%. Strong keratolytic: 20-40%. For face: stay at 5-10%. For body rough patches: 10-20%. For calluses/severely rough skin: 40%. Apply to damp skin and seal with cream. |
| Application | Topical (cream, lotion, serum). Best in emollient/occlusve formulations rather than water-based serums. | Topical (cream, lotion, gel). Apply to damp skin. Eucerin and CeraVe have well-known urea-containing lines. |
| Research Papers | 10 papers | 10 papers |
| Categories |
Mechanism of Action
Ceramides
Ceramides are sphingolipids comprising a sphingoid base (sphingosine or phytosphingosine) amide-linked to a fatty acid—comprising ~50% of stratum corneum lipids. They integrate into the intercellular lipid matrix between corneocytes, forming the lamellar bilayer structure with cholesterol and free fatty acids that limits transepidermal water loss (TEWL). Optimal molar ratio is ~3:1:1 (ceramides:cholesterol:fatty acids). Topical ceramides (NP/3, AP/6-II, EOP/1) fill gaps from barrier damage by surfactants, retinoids, or inflammation. Cholesterol enables lamellar phase formation; fatty acids provide acidic pH for ceramide packing. Products restoring the complete ratio upregulate barrier repair genes (involucrin, filaggrin, transglutaminase) more effectively. Synthesis occurs via serine palmitoyltransferase and ceramide synthase in keratinocytes.
Urea
At low concentrations (<10%), urea acts as a humectant — small molecule (60 Da) absorbing into stratum corneum, drawing water via hydrogen bonding to carbonyl and amine groups. Part of endogenous NMF (filaggrin degradation products with amino acids, lactate), highly biocompatible. Integrates into corneocyte envelope, supports aquaporin-3 water transport. At higher concentrations (>10%), denatures keratin (K1, K10) by disrupting hydrogen bonds in alpha-helical structure and disulfide bridges in cornified envelope, causing corneodesmosome degradation and desquamation. Keratolytic via direct protein denaturation, not enzymatic. Dual mechanism — humectant at low dose, keratolytic at high — versatile for hydration and hyperkeratotic conditions (psoriasis, keratosis pilaris).
Risks & Safety
Ceramides
Common
Essentially none — ceramides are bioidentical to skin components.
Serious
None. Safe for all skin types including sensitive, eczema-prone, and rosacea.
Rare
Virtually no risk.
Urea
Common
Stinging on broken or irritated skin (more likely at higher concentrations).
Serious
None.
Rare
Contact dermatitis (uncommon).
Full Profiles
Ceramides →
Lipids that make up approximately 50% of the skin barrier by weight. Ceramides form the 'mortar' between skin cells (the 'bricks'), creating a waterproof barrier that prevents water loss and keeps irritants out. When the skin barrier is damaged — from over-exfoliation, harsh cleansers, retinoid use, or conditions like eczema — ceramide levels are depleted, and replenishing them is essential for recovery.
Urea →
A natural component of the skin's Natural Moisturizing Factor (NMF) that serves as both a humectant and a keratolytic depending on concentration. At low concentrations (2-10%), urea hydrates by drawing water into the stratum corneum. At higher concentrations (20-40%), it breaks down keratin protein, making it a powerful treatment for rough, thickened, or keratotic skin conditions like keratosis pilaris, calluses, and psoriasis.