What the Stratum Corneum Has to Do With Zinc

A Boundary Layer With a Structure of Its Own

Seen from the outside, skin looks like a single, uniform covering. Under a microscope, a layered structure appears: the epidermis with its several cell layers, beneath it the dermis with blood vessels and nerve endings, and beneath that the subcutaneous fat layer. Each of these layers takes on its own job within the overall system.

Trace elements act as cofactors at several points within this structure. For zinc, the European Commission has authorized a health-related claim linked to skin, based on a scientific opinion from the European Food Safety Authority (EFSA). The next two sections set out exactly where this trace element shows up.

Moving the Metal Ion Through the Cell Layers

Zinc reaches the skin by way of the bloodstream, but from there it still has to make its way into the individual cell layers of the epidermis — from the basal layer, where new cells form, to the stratum corneum at the surface. Specialized transport proteins from two large families handle this: ZIP proteins move zinc into the cell interior, while ZnT proteins move it back out again or into internal cell structures.

Both protein families occur in a different mix within each cell layer, which is why the local zinc concentration differs from one layer to the next. The scientific literature describes this fine-grained distribution as a precondition for the many zinc-dependent processes in skin to run at all.

Why the Skin's Surface Stays at a Low pH

Part of what the sweat glands secrete is co-determined by a zinc-dependent enzyme called carbonic anhydrase. This enzyme influences how much the sweat reaching the skin lowers the pH there. Under ordinary conditions, this keeps the skin's surface in the slightly acidic range — a state the scientific literature often describes as part of the tissue's outermost boundary.

The two points described here — the distribution of the metal ion itself and a downstream enzyme effect — concern different levels of the same tissue. The official wording doesn't distinguish between them and only describes the documented overall result:

Amount, Source, and What Everyday Food Provides

For adults, EU labeling regulation 1169/2011 sets a daily reference value of 10 mg of zinc. How much of that a given food provides, though, differs considerably:

Zinc content of selected foods (approximate values per typical serving)

Food	Approximate contribution to the daily reference value
Oysters	very high
Beef liver	high
Cashews	moderate
Chickpeas	moderate
Whole-grain oats	low to moderate
Egg yolk	low

Plant sources supply zinc together with phytic acid, which binds part of it in the small intestine and slightly reduces absorption. Soaking or sprouting legumes and grains before preparing them lowers their phytic acid content and helps absorption a little.

With a mixed diet that includes both animal and plant foods, the daily reference value can usually be reached without an extra product. Anyone eating exclusively plant-based can benefit from individual guidance to better judge their own intake.

Questions That Come Up About This Claim