Sebum

The natural oil your skin makes to stay moisturized and protected — its name literally means 'tallow' in Latin.

Sebum is the oil your skin produces to keep itself supple, resilient, and shielded. Made in the sebaceous glands, it spreads across the stratum corneum, the outermost layer of the skin barrier, where it joins ceramides and cholesterol in the lipid matrix that slows transepidermal water loss (TEWL). It's roughly 57% lipids, of which about 44% are saturated fats, with oleic, palmitic, and stearic acid among the key players. As skin matures, especially through perimenopause and menopause, it makes less sebum, which is part of why mature skin can feel drier, thinner, and more fragile. Grass-fed tallow is compelling precisely because its fatty-acid profile is so close to sebum's that skin treats it as familiar.