Drying stresses and cracked skin: The importance of afore skin rituals

The apres ski process may involve joining friends around the warmth of a fire, where glasses filled with various libations clink against a background of discourse related to the conditions of the day. Inevitably, ski week produces its share of cracked lips and chapped skin amidst this revelry. How?

The stratum corneum (SC) is the outermost layer of skin. It is 10-20 micron-thin and made of lipids and proteins. Extending just one percent of the entire skin layer thickness (epidermis and dermis), the SC serves as the primary protective barrier- keeping moisture in and environmental toxins out. The SC structure, when formed properly by healthy skin, is often described as a brick and mortar structure where corneocytes, the bricks, are contained within a continuous phase of lipid lamellae, the mortar. The lipid lamellae are composed of multiple layers of lipid bilayers where the greasy parts of the lipid face each other, directing the more polar, water-liking, part of the lipid to align on the outside of the bilayer. 

The corneocytes are approximately 40 microns in diameter and about 0.5 microns thick. There are 15-25 layers at most skin sites. The soles are substantially thicker, for instance. To help us visualize this model, we asked Gemini to generate schematics of the brick and mortar architecture (above), in addition to the lipid bilayer structure (below).

Visualizing the skin through this model, helps us see that it is much more complex than a single protective layer, and that lipid fluidity is one factor that influences the stresses placed on the stratum corneum. 

For example, humectants such as glycerin can increase the fluidity of the lipid bilayers, decreasing the stiffness to impart more flexibility and elasticity. Moreover, occlusive ingredients such as petrolatum and dimethicones can achieve a similar effect by reducing the loss of moisture vapor from the skin. Studies have shown that increasing the relative humidity correlates with decreasing the stiffness of the stratum corneum, and thereby increasing its pliability. 

One measure of this stiffness is called the modulus. In one study, as the relative humidity was increased from 20% RH to 100% RH, the SC modulus was seen to decrease as much as 20 fold. Generally speaking, the stiffer the material, the less pliable and more brittle it is.

In dry conditions, such as a day filled with high velocity, lengthy ski runs, the SC wants to shrink due to moisture loss. Because the SC is attached to the underlying skin layers and held in place, the need to contract creates a stress that induces SC crack propagation.

While the apres ski ritual may be the emphasis following some epic skiing, remember the afore ski ritual of proper moisturization to subdue those drying stresses and keep those skin cracks at bay.

Posted March 1, 2026.