An inside look at baby’s skin

Baby skin is the result of a long growth process that takes place throught pregnancy

Around the 40th day of pregnancy, the tiny embryo measures just 10 – 14 mm. The tongue appears, teeth begin to grow and the baby’s epidermis begins to develop.

By the 22nd week of pregnancy, the baby measures 17 cm from the head to the base of the spine, 26 cm from head to heel and weighs 500 grams. The skin begins to get thicker, but it is not yet wrinkled because there is still no subcutaneous fat. Sebaceous glands form and begin to secrete a waxy substance called vernix caseosa to protect baby’s skin while submersed in amniotic liquid.

Subcutaneous fat appears in the 23rd week of pregnancy, as do the little lines on baby’s fingers and palms that will eventually become fingerprints. Dental buds are in place and the ivory of future baby teeth begins to form.

In the 35th week, baby now measures 30 cm from the head to the base of the spine, 45 cm from head to heel and weighs around 2.4 kg. The baby rounds out continously. Vernix is still present, and the baby will undoubtedly still have some at birth (these are the little white marks that you can see on baby’s skin when you first take him or her in your arms).

By the 36th week of pregnancy, the baby measures 32 cm from the head to the base of the spine, 46.5 cm from head to heel and weighs around 2.65 kg. Soon baby is going to meet his or her parents, and the skin has now reached a point where it is strong enough that mommy and daddy could touch it.

The physiology of baby skin is quite particular :

When the baby is born at term, baby skin is incomparably soft, fine and easily irritated: the corneum layer (outermost layer), epidermis, dermis, and hypodermis are all in place.

However, baby skin is quite different from adult skin :

– The skin’s corneum layer is fine and permeable. The dermis is not as thick as an adult’s. It is composed of fine, flexible fibres and very thin collagen fibres. The child’s skin won’t become a barrier that is almost entirely impermeable until the age of 4. Until then skin is easily irritated and represents an easy point of entry for chemical agents. It does not yet possess the natural defence mechanisms that compose its structure upon maturity: any untreated lesion can be the source of infection. It is estimated that a cutaneous flora of 50 – 60 million bacteria thrive per square centimetre of baby’s skin.

– Sudiparous glands are not yet ready to function “correctly.” New-borns have a natural sweat deficit, meaning that that have a hard time eliminating waste and toxins, and regulating body temperature. Less lubricated, skin has more of a tendency to dry out.

– Sebaceous glands, stimulated during pregnancy by maternal hormones, are over-developed at birth, resulting in an excess of sebum. This is one of the reasons for “baby scab” (croûtes de lait), for example. Over the first few months, baby’s skin will change and become increasingly drier until puberty.

– Covered with a hydrolipid film that is too thin and not resistant enough, baby skin is particularly sensitive to outside aggression, such as from wind, heat and the rubbing of diapers and clothes.

– There are still not enough pigmentation cells, melanocyte cells responsible for giving skin its colour, which is why many children have a very clear tint at birth even if that is not the case for his or her parents.

– Baby skin lacks melanin, a substance that protects against ultraviolet rays, and is therefore extremely sensitive to aggression from the sun.

– For babies just a few weeks old, the sweating mechanism involved in thermoregulation is not yet well developed. Therefore, tiny newborns are more vulnerable to temperature variations than adults.

Dr Philippe Goëb

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