Dr Ian Webster
Dr Ian Webster

The Evolution of the Skin

The most favoured theory about human evolution is that man or Homo sapiens originated in Africa. We think that the first waves of migration out of Africa took place about 80 000 years ago into the Mediterranean followed by the Indian sub-continent and Asia. Migration to Western Europe happened relatively late, only about 40 000 years ago.

We assume that man who left Africa had darker skin (human fossils give no indication of skin colour). The more melanin pigment in the skin, the greater the protection from strong ultraviolet radiation. Vitamin D is required for the normal, healthy functioning of the human body and it is derived from two sources: namely diet and from UVB reacting in the skin to produce Vitamin D. A paler skin is more efficient at producing Vitamin D in the skin from UVB radiation than a darker skin.

As man migrated northwards to countries where the UVB levels were very low, it would have been an evolutionary advantage to have paler skin. Humans living in the northern hemisphere, with darker skin, had a greater chance of developing rickets in childhood. In women, rickets could have caused abnormal pelvic bones and put the mother at a higher risk of dying in childbirth. Therefore, the humans with the darker skins, through natural evolution would have died off, favouring genetic mutations with a paler skin. An example is the Scottish Celtic skin with reddish blonde hair.

Thus, humans with a paler skin were able to survive in the northern hemisphere without getting rickets, so the women were less likely to die in childbirth and a paler skin was, therefore, an evolutionary advantage.

The exceptions to this are the Inuit or Eskimos who have a darker skin but live on the coastal areas in the northern hemisphere. The reason that they have been able to survive with a darker skin and limited UVB exposure is that their diets are rich in Vitamin D as a result of the ingestion of oily fish.

So how does the environment today impact on the skin?

Ozone is a gas that occurs both in the earth’s upper atmosphere and at ground level. The upper atmosphere ozone is called Stratospheric ozone and is a good ozone in that it protects life on earth from the sun’s harmful ultraviolet radiation. However, this good Stratospheric ozone is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances. These ozone-depleting substances cause a hole in the ozone layer and this is mainly formed in the Antarctic. This hole moves around depending upon polar winds and different seasons of the year.

As a result of the hole in the Stratospheric ozone layer, the highest UV levels are generally found in countries in the South Hemisphere such as South America, South Africa, Australia, and New Zealand.

People with a paler skin born in these countries in the southern hemisphere have the highest incidence of photo-ageing and skin cancer in the world, while people with a darker skin have less of a risk.

Conversely, people with a darker skin, who were born and live in the northern hemisphere, are more at risk of developing a Vitamin D deficiency and the health consequences thereof: Vitamin D is needed for the healthy functioning of all the organs in the body, including the immune system and bones.

It is very important that people with a paler skin practice sun avoidance, regularly use a high factor, broad-spectrum sunscreen together with added sun protection: a UV protective hat and clothing.

The other type of ozone is the ozone that occurs close to the earth’s surface and this is called Tropospheric ground level or bad ozone. This is essentially due to air pollution and is damaging to trees, crops, lungs and to the skin. It is potentially carcinogenic and causes what is termed Atmospheric Ageing. This ground level ozone may impair the skin barrier function (lipid peroxidation), cause pigmentary changes as well collagen degradation resulting in accelerated wrinkle formation. Air pollution can also cause excessive oiliness, rougher skin texture and increased sensitivity.

Unfortunately, the good Stratospheric ozone is being depleted and the bad Tropospheric ozone is generally increasing. The only really effective way of combating the bad or ground-level ozone is to use a good, correctly formulated antioxidant every morning, together or combined with a high factor, broad-spectrum sunscreen for protection against UV radiation.

For those with a darker skin and who live in the northern hemisphere, it might be worthwhile checking their Vitamin D levels in the blood and if it is low, to take a Vitamin D supplementation orally.

The normal healthy surface of the human skin has millions of bacteria, fungi, viruses, and mites. This is called the skin microbiome and is very important for the normal, healthy functioning of the skin. There is a lot of diversity of the skin microbiome that varies from individual to individual and this can be likened to a unique fingerprint. Ultraviolet radiation, pollution, the use of anti-bacterial soaps with the wrong pH and oral antibiotics will alter the skin microbiome. A child born by normal vaginal delivery will have a healthier skin microbiome than a child delivered by cesarean section. Therefore, the ideal skin care products to help to preserve the normal skin microbiome would be gentle products that are pH 5.5. There are some products that contain natural thermal spring water which acts as a prebiotic and some that contain heat-killed strains of bacteria which act as a postbiotic.

The very top layer of the skin is called the stratum corneum and this contains a lipid layer that retains moisture and protects the skin from outside environmental influences. Pollution and ground-level ozone can disrupt the normal epidermal layer of lipids and cause loss of the normal barrier function of the skin resulting in dryness and dehydration. If this lipid layer has been damaged they should ideally be replaced by lipids that mimic normally occurring lipids in the skin i.e. these lipids need to be the right lipids, at the right concentration and at the right ratio to each i.e. the so-called golden ratio: 2% ceramides, 4% natural cholesterol & 2% fatty acids. Skincare products that contain these lipids in the correct ratio will help to restore the normal, healthy functioning of the skin.

Today we have some advanced skincare products that protect against UVB, UVA, High Energy Visible Light as well as Infrared radiation. In addition, they contain antioxidants that protect against pollution and ground-level ozone. There are a handful of skincare products in the world that in addition to the previously mentioned constituents, contain enzymes that can remarkably repair damaged DNA. A lifetime of sun exposure damages the DNA in the cells in the epidermis and this can lead to pre-cancerous lesions such as actinic keratoses or frank skin cancer such as basal cell carcinoma or squamous cell carcinoma.

These products are called sunscreens but in fact, they are far more advanced than that as they prevent, repair and eliminate DNA damage, going far beyond normal photoprotection. They protect against pollution, ground-level ozone, infrared radiation and can repair damaged DNA.

Anyone with chronic sun-damaged skin and who has had actinic keratoses or skin cancer should be using one of these products on a daily basis.

Posted in LEARN / SKIN ANATOMY on March 14th, 2019.

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