Water moves through the body and serves its internal needs, then moves to the surface
of the skin in a process called, “transepidermal water loss” (TEWL). Well-balanced
skin maintains a healthy TEWL, leaving skin pleasingly plump and firm, and well
hydrated. Water comprises up to 75% of the skin’s overall weight, but only 10-15%
of the stratum corneum. If the body lacks adequate water, the skin’s outer layers
become dry and brittle. If the water content of the epidermis falls below 10%, it
becomes dry, less flexible, and increasingly prone to damage, breakdown, and infection.
Drinking at least six glasses of water daily and eating fluid-rich fruits and vegetables
helps normalize dry or oily conditions, and is essential to the moisture balance
in the body and in the skin. The epidermis is about 35 micrometers thick when dry
and dehydrated, but can swell to 48 micrometers when fully hydrated.
The skin also requires external water replenishment. Topical products such as sodium
hyaluronate, sodium PCA, sorbitol, glycerine, and propylene glycol are designed
to maintain hydration.