Free ceramide levels in the stratum corneum change with seasonal influences. The level of covalently-bound ceramides can halve in the winter compared to the summer. In addition, saturated fatty acid ceramides see a greater decrease in the winter compared to unsaturated fatty acid ceramides, meaning the ratio between them changes over the year.12

Protective NMF levels can also change over the year, accompanied with changes in corneocyte surface texture, depending on the conditions the skin is exposed to. NMF levels in the cheek epidermis can fall in winter with cells shrinking and cell surfaces becoming more wrinkled.17

For hand skin, NMF levels may actually increase in winter if protected, so the shrinkage effect on skin cell texture is more likely to arise in summer through UV exposure.

Blood circulation in the skin is also affected by temperature, with peripheral blood vessels contracting when exposed to the cold. While reduced blood flow in the dermis was thought to be the cause of dry skin in cold weather, the relationship appears to be more about the recovery rate for the skin temperature returning to normal after exposure to the cold.18

People with a high/fast skin temperature recovery rate show less of a change in skin dryness between summer and winter than those with a low recovery rate. The recovery rate is associated with increased trans-epidermal water loss and the reduced amount of moisture in the stratum corneum.