“Smooth as a baby’s bottom” summarizes the popular notion of infant skin: the soft, supple, and practically flawless integument that is the unattainable objective of all cosmetic treatments. Indeed, it can be difficult to imagine what problems a paediatric dermatologist could possibly address given how perfect new-born skin appears to be. And while there are undoubtedly plenty of skin maladies that affect those at the beginning of life, even for the smoothest of bottoms, there are critical differences worth thinking about, both in health and disease. In this article, we review some of the important structural and physiologic differences between infant (defined here as the first few years of life) and adult skin. We also consider some of the clinical and practical ramifications of these distinctions using evidence whenever possible.
The functions of the skin remain essentially the same at all phases of life however; there are several important structural differences between the skin of babies and adults. Barrier function of the skin is vital for survival for all human beings. Increased skin absorption of chemicals greatly increases mortality in premature infants due to microbial invasion.
Barrier development continues during the first year of life as infant skin is able to absorb and lose water faster than adult skin. Other microstructural differences include thinner stratum corneum and papillary dermis in infant skin; however, several factors make infants more susceptible to percutaneous toxicity. Their high surface area-to-volume ratio, immature drug metabolism systems, and decreased subcutaneous fat stores effectively increase the absorptive area while decreasing the volume of distribution of a drug or toxin. This is compounded by the fact that once absorbed, the infants lack fully developed drug carriage and detoxification systems. Furthermore, direct barrier injury can occur because of the increased fragility of infant skin, thus increasing local permeability. Finally, given the estimated 20% incidence of atopic dermatitis among children, there are other reasons for barrier function to be impaired at baseline. Because of these factors, it seems prudent to advise that only essential products be applied to the skin, particularly in the first several months of life.
Bathing an infant provides important psychological benefits between parent and child. However, oddly enough, it can also provide an opportunity to damage the skin. There is evidence to suggest that washing the skin with a washcloth during the first 4 weeks of life is associated with increased TEWL [trans-epidermal water loss] and decreased stratum corneum hydration compared with simply soaking in water. Another study found that tub bathing an infant was actually associated with an increased risk of cord infection vs no washing at all. Several papers have examined the use of mild liquid cleansers vs using water alone for bathing. The consensus appears to be that a mild liquid cleanser may actually be less drying and less irritating than water alone, and that bathing should be brief (10 minutes or less) and no more than every other day with spot cleaning in between.
Infant skin is often thought of as ideal skin, and its characteristics are frequently sought by adults. However, beyond the smooth and supple beauty, there are significant structural and functional differences that make infant skin more susceptible to certain problems. During the first years of life, there are considerable developments of the skin and subcutaneous fat that warrant handling infants differently—and much more gingerly—than adults.
Summary of CME/CE Information