The functions of the skin

Skin has many functions. Some of these functions are so important that unless most of the skin is working efficiently, we would not survive.

The functions of the skin include

Sensation
Heat regulation
Absorption
Protection
Excretion
Secretion

The functions of the skin are often referred to as SHAPES. We tend to think of the skin as a single organ. The epidermis and dermis have, to some extent, separate functions. The function of water conservation is, however, dependent on both. The role of the stratum corneum in this field is vital as it acts as a semi permeable barrier and allows us to survive in a hostile environment.

Functions of the epidermis

There are three principal functions:

Protecting the body from the environment, particularly the sun
Preventing excessive water loss from the body
Protecting the body from infection

Functions of the dermis

giving protection to the body from bumps and knocks
removing waste products of metabolism from the epidermis, which are also carried away in the blood
providing shape and form to the body, by holding all its structures together
contributing to skin colour, particularly in people with little melanin in the epidermis
regulation of body temperature through control of blood flow and sweating
· skin sensations of touch, pain, heat and cold through nerve endings

Functions of the skin

Secretion: Sebaceous glands secrete sebum which coats the skin’s surface and helps to waterproof it, at the same time slowing down the evaporation of moisture from within. It also creates a barrier, known as the acid mantle, which inhibits the growth of harmful bacteria. This is the gland that can over secrete and cause the skin to be too oily.

Heat regulator: To compensate for changing temperatures outside the body, the blood and sweat glands make the necessary adjustments to their functions, thereby maintaining the normal temperature of a healthy body, 36.5-37.5 degrees Celsius. The body also has a system of controlling the blood vessel size. When we get hot they vasodilate, get bigger, to allow the blood to be near the surface of the skin to encourage heat loss. The opposite of this is vasoconstriction, they get slimmer, to keep the heat inside. This is why we can look paler as there is less blood near the surface of the skin. Also the hairs react when we are cold causing them to stand up to try and trap warmer air near the surface of the skin, we can see this as ‘goosebumps’.

Absorption: The skin has only limited powers of absorption. However some chemicals, cosmetics and drugs can be absorbed in small amounts through its pores. What the skin does absorb is ultra-violet light (UV), sunlight. UV absorbed through the skin is converted into molecules that will be converted into Vitamin D through processes in the liver and kidneys. Vitamin D is good for teeth and bones. This can also be an double edged sword with too much exposure. 20 minutes is usually sufficient enough for paler skin tones but increases to 40 minutes for darker skin tones due to the fact that they have more melanin present in the skin so it will take longer to penetrate into the skin.

Protection: The skin protects the body from bacterial infection and injury. Melanin protects the skin against ultra violet radiation and is responsible for the differences in skin colour. Exposure to sunlight increases the production of melanin as the skin works harder to increase its protection levels; the visible evidence of this is a sun tan.

Protection from the environment

The sun produces enormous amounts of heat and light, some of which reaches the earth. Without this heat and light, no life could ever have evolved.

Unfortunately, the sun also produces less beneficial rays, which are invisible to us, called ultraviolet radiation (sun beds also expose their users to these rays). Part of this radiation is reflected by the stratum corneum at the skin’s surface, part is absorbed by the melanin in the epidermal cells, and some is scattered within the skin. All three processes contribute to protecting the nuclei of the cells in the epidermis and the collagen of the dermis.

This scattered radiation creates a lot of high-energy particles, which are called free radicals. Free radicals are very reactive, and attack the constituents of the skin: this is why over a long time ultraviolet radiation produces so much damage.

Prevention of water loss from our skin

Throughout our lives our bodies naturally lose water by constant gentle evaporation through our skin.

Preventing excessive water loss is exceptionally important in itself – both to the skin itself and to the body as a whole. In the normal epidermis the water content becomes lower the closer we get to the surface. Water makes up 70-75% of the weight of the basal layer, but only 10-15% of the stratum corneum. The stratum corneum is a particularly important barrier to the control of moisture loss.

It is also a highly effective barrier against the outside environment, being tough but flexible provided it is well hydrated. If its water content falls below 10% it becomes dry, less flexible and increasingly prone to damage, breakdown and infection.

Preventing infection

The natural layer of oil-in-water emulsion on the skin is the first barrier against invasion by micro-organisms such as bacteria, fungi and yeasts. The stratum corneum provides the next level of defence.

White blood cells in the skin can capture and destroy bacteria invading the epidermis. As a result pus may form.

The epidermis also contains special defence cells (Langerhans cells) which are spread out amongst the keratinocytes. These cells mop up invading substances found in the body and take them to special white blood cells called lymphocytes, which are found in lymph glands. Here they are then neutralised.

An important element of defence concerns chemicals. If a chemical such as nickel is constantly absorbed through the skin, say from a button on one’s jeans, it is first taken up by the Langerhans cells. However later special lymphocytes called T-cells make antibodies to that chemical. This can in time lead to an allergic skin reaction at the site of the button as the T-cells rush to meet the invading chemical.

Excretion: Sudoriferous glands (sweat glands) excrete perspiration which is waste matter, this is why a lot of treatments in spa’s are designed to hot to induce this detox. The mixing of sweat and sebum on the skin’s surface forms the protective layer of the acid mantle. There are 2 types of sudoriferous glands in the body. Eccrine glands are smaller and found all over the body, Apocrine glands are bigger and are found in hairy areas like underarms and scalp.

Sensation: Heat, cold, pain, pressure and touch receptors are found in the papillary layer of the dermis. Nerves supplying the skin register these basic sensations. Therefor if something is hot we pull away from the heat source.