What do ceramides actually do for your skin?

The short answer: ceramides seal your skin

Ceramides are the main structural lipid of the outermost skin layer. Think of them as the mortar in a brick wall: skin cells are the bricks, and lipids fill the gaps so water stays in and irritants stay out. The structural role is the best-supported part of the story, as a review of ceramide abnormalities in atopic dermatitis lays out in its brick-and-mortar model.

The mortar is mostly ceramide, with cholesterol and fatty acids

Ceramides make up roughly half of the outer layer's lipids. Cholesterol accounts for about 25% and free fatty acids for about 15%. One review puts the mix at 50% ceramides, 25% cholesterol and 15% free fatty acids, with very little phospholipid, according to a review of the Elias barrier work and a thematic review of epidermal lipids.

Chemically, a ceramide is a long-chain base joined to a fatty acid by an amide bond. What makes them interesting is variety. A 2022 LC/MS/MS study of human stratum corneum quantified 1,327 unprotein-bound and 254 protein-bound ceramide species, the largest number reported to date.

Among species with long-chain bases of C16 to C26, C18 made up 28.6%, C20 24.8% and C22 12.8%. Those are shares within that chain-length group, not shares of total ceramide mass, so don't quote them as the whole picture. The authors link this chain-length diversity in the outer layer to barrier performance.

What happens when ceramides drop: lab models say a lot

The clearest mechanistic evidence comes from lab models, not people. In lipid models built from isolated human outer-layer ceramides, cutting ceramides by at least 30% significantly raised permeability to four markers. The authors attribute this to lost long-periodicity lamellae and phase separation, per a study of lysosphingolipids in ceramide-deficient skin models.

Swapping in lysosphingolipids and free fatty acids for the missing ceramides added no further permeability increase. Adding 5% to 10% sphingosine-phosphorylcholine partly offset the damage. Blocking ceramide synthesis also impairs lamellar body formation, which disrupts barrier homeostasis, as the thematic review on epidermal lipids describes.

Lower ceramides show up in skin conditions, but that isn't proof of cause

Reduced barrier function is linked to infection, atopic dermatitis, xerosis and ichthyosis. A decrease in ceramide levels, or a shift in their composition, is associated with atopic dermatitis and psoriasis. These are observational links, so we read them as signals, not settled cause and effect.

In dry skin, ceramides are described as the most abundant intercellular lipids, reaching up to 50% of outer-layer lipids. A recent LC-MS/MS study of normal and dry skin subtypes links abnormal ceramide chain lengths in dry subtypes to compromised barrier integrity and greater inflammatory susceptibility. That is a mechanistic association, not proof that chain changes cause dryness.

Topical ceramide products: the evidence is thin

Bottom line: we found no human trials or meta-analyses of topical ceramide moisturizers in this search. We can't tell you how much they help, or whether they improve water loss measures in people. A structural role inside skin doesn't automatically make a cream effective.

One porcine ex vivo study looked at sorbitan esters. It found no significant change in transepidermal water loss, and the least ceramide depletion came from sorbitan ester 60 and cholesterol treatments. The authors judged the esters skin-friendly, per a porcine ceramide profiling study. Pig skin doesn't map cleanly onto human skin, so treat that as a lab result.