Infant skin physiology and development during the first years of life: a review of recent findings based on in vivo studies.

Infant skin is often presented as the cosmetic ideal for adults. However, compared to adult skin it seems to be more prone to develop certain pathological conditions, such as atopic dermatitis and irritant contact dermatitis. Therefore, understanding the physiology of healthy infant skin as a point of reference is of interest both from the cosmetic as well as from the clinical point of view. Clinical research on healthy infants is, however, limited because of ethical considerations of using invasive methods and therefore until recently data has been scarce. Technical innovations and the availability of non-invasive in vivo techniques, such as evaporimetry, electrical impedance measurement, in vivo video and confocal microscopy, and in vivo fibre-optic based spectroscopy, opened up the field of in vivo infant skin physiology research. Studies incorporating such methods have demonstrated that compared to adult, infant skin continues to develop during the first years of life. Specifically, infant skin appears to have thinner epidermis and stratum corneum (SC) as well as smaller corneocytes at least until the second year of life. The water-handling properties are not fully developed before the end of the first year and infant SC contains more water and less amounts of natural moisturizing factors. Such findings re-evaluate the old notions that skin is fully matured at birth. Armed with this knowledge, we are in a position not only to better understand infant dermatological conditions but also to design better skin care products respecting the distinct qualities of infant skin.