A child’s skin is not a miniature version of an adult’s: it is an organ in full development, whose structures and functions are progressively established over the years. From birth until roughly six years of age, the skin barrier strengthens, cells renew at a rapid rate and the microbiome gradually stabilises. These transformations, both microscopic and visible, shape the skin to prepare it for its mission: protecting the body from the external environment.
In the newborn, the skin is thin, permeable and particularly vulnerable to environmental insults. The stratum corneum consists of loosely packed lipids and small corneocytes, which makes the skin barrier less effective than in adulthood. Water loss through the skin is thus higher, which explains infants’ tendency to exhibit dry skin. As growth continues, the skin becomes thicker and more resilient. By the age of six, stratum corneum thickness, water loss and corneocyte size reach levels comparable to those of adults.
Moreover, during early childhood, cellular metabolism is sustained by the high proliferation of keratinocytes. Similarly, melanocyte activity, the cells that produce melanin, gradually increases. Children’s complexions become slightly darker, while the skin thickens and gains resistance to UV radiation. However, this developing skin remains highly sensitive to the sun. The melanogenesis is not yet optimal and the defence mechanisms against free radicals are immature. This is why it is very important not to expose the children to the sun.
Finally, the skin microbial ecosystem undergoes a gradual progression as well. In infants and young children, bacteria of the phylum Firmicutesdominate the skin flora, whereas in adults it is primarily the Proteobacteriaand the Actinobacteriathat predominate. Microbial diversity increases and gradually stabilises, allowing immunity to strengthen.