Vernix caseosa is a layer that is formed in the womb in the last trimester of the baby's development and wraps the skin from top to bottom. It contains 80% water, 10% protein and 10% lipids. This layer prevents the contact of the epidermis with water and creates a dry environment, therefore allowing the formation of the stratum corneum protective barrier. In a study, if the vernix was not removed immediately, it was observed that the skin was moistened a further 24 hours after birth and the skin PH is decreased. In model systems, it was observed that the vernix protects the skin against many pathogenic microorganisms. Vernix also contains cholesterol, ceramide, and many fatty acids. In particular, the anti-inflammatory linoleic acid enhances the rate of barrier formation by activating the peroxisome proliferator-activated receptor alpha. Therefore, the World Health Organization recommends that the vernix layer is not removed at least 6 hours after birth.

Skin hydration quickly decreases on the first day after birth, then increases for 2 weeks. These changes indicate that the skin is adapting to the new environment. An acidic environment is required for the function of enzymes that provide the formation and integrity of the stratum corneum, for lipid metabolism, ceramide synthesis, exfoliation, inhibition of pathogenic bacteria. The skin of an infant born at the full term is neutral at birth and decreases significantly within the first 1-4 days and continues to decrease in the first 3 months. Acidification is necessary for the fusion of free fatty acids and stratum corneum cells. Skin thickness, acidity, moisturizing adapts in the first weeks and months of life. However, these do not indicate complete barrier function in the infants.

In premature babies, especially in the ones that were born with very low weight, the skin barriers are very weak, the skin proteins are lacking. Therefore, they are at risk of skin damage, the permeability to external agents and infections is increased.