Dry Skin

Dry Skin

Two deficits underlie the measurement. Natural moisturizing factor, the mixture of amino acids and their derivatives generated by filaggrin breakdown, holds water inside corneocytes; when it is depleted the cells cannot retain hydration. Separately, the lipid bilayer between corneocytes loses ceramides and free fatty acids, so evaporation accelerates from a barrier designed to slow it. Tight or rough texture, visible flaking, itching and fine cracks follow from both.

Collagen peptides hold Grade B on 14 studies and 920 participants. Hydration is a more tractable endpoint than wrinkle depth and responds within weeks in most protocols, which is why the rating sits higher for this condition than the mechanism alone would predict. Hyaluronic acid follows at Grade B on 10 studies and 620 participants, with oral administration presenting an obvious question about a molecule too large to cross the gut intact; the working account involves degradation to smaller fragments that are absorbed and may act as signals to dermal fibroblasts rather than as delivered substrate.

Ceramides at Grade C on 5 studies and 300 participants have the most direct rationale of any entry, since they are the same lipid class the barrier is short of, though oral delivery to the stratum corneum is an indirect route to a topical deficit. Lactobacillus plantarum holds Grade C on 3 studies and 180 participants through the gut-skin axis, and biotin sits at Grade D on 2 studies and 100 participants, a rating consistent with the observation that biotin supplementation is well studied in genuine deficiency and poorly studied in its absence. A systematic review and meta-analysis of randomized controlled trials found that oral supplementation can produce measurable improvement in skin moisture in healthy adults, while noting substantial heterogeneity between the products tested ^[1].

Environment usually outweighs supplementation. Low ambient humidity, cold weather and frequent washing with surfactant cleansers strip barrier lipids faster than any oral intervention rebuilds them, and trials conducted across a change of season carry a confound that is rarely controlled.

Dry skin is also a presenting sign of conditions that are not dermatologic. Hypothyroidism, diabetes and nutritional deficiency each produce xerosis, so skin that becomes persistently dry without an environmental explanation is a reason for medical assessment rather than for a longer supplement regimen.