Human Skin Types
One way in which scientists define skin type is according to how it responds to exposure to the sun.
The system of classifying skin according to its type, shown in the table above, was developed on a two-factor basis: hair color and the ability to tan. Classification under this system also indicates the people who are especially prone to develop skin cancer. The six-point scale is based on the answers people give when questioned about how they react to sun exposure.
Individuals who are types I and II have skin more likely to burn and have difficulty developing a tan. It is also these people who are at highest risk for the development of skin cancer. During the last two centuries or so, many people of this type have moved to sunny climates like those of Australia and South Africa and are now at a much higher risk of developing skin cancer than if they had stayed in Europe.
Skin type descriptions
Another way of classifying skin types becomes evident when people are asked to describe how they view their skins. For practical rather than necessarily scientific proposes, they will often describe their skin type as either normal, dry, greasy or mixed.
In the next part of this chapter we discuss each of these descriptions in turn.
Normal skin that sometimes burns but eventually tans. Auburn hair and blue eyes are typical of north-western Europe and parts of the populations of countries such as North America, Australasia and South Africa. This type of skin is susceptible to the long-term effect of the sun.
The characteristics of so-called 'normal' skin can be summarised as follows:
- a clear appearance
- an even color
- feels neither tight nor greasy
- soft and supple to the touch
- a high degree of elasticity.
Normal skin may be said to have nothing obviously wrong with it, and no sensations of discomfort. It results from a balance of the normal skin functions (including new skin cells being formed and old ones being lost, together with well-controlled water loss, sebum secretion and sweating). This creates a balanced state of suppleness, elasticity, color and hue which is often characteristic of pre-adolescents.
Normal skin can quite quickly become 'abnormal', however. Failure to look after it, or abuse by sun, wind or cold, may lead to dry and damaged skin and ultimately the risk of premature development of lines and wrinkles.
- feels tight and irritable
- often looks flaky
- often develops fine lines around the eyes
- tightens after washing with soaps or detergents or prolonged exposure to low humidity.
Dry skin is characterised most of all by this sensation of tightness, with the skin feeling rough and scaly and visible lines developing. At its worst it may look cracked. The problem lies in poor epidermal function and damage to the water/lipid barrier film, shown by an increase in the rate of transepidermal water loss (TEWL).
Patches of dry skin may arise from apparently normal skin, or sometimes even greasy skin, that has been temporarily dried out, whether by sunburn, or by exposure to extremes of climate (cold, heat, wind or dryness) or to chemicals such as detergents and solvents or to air conditioning. In young people the main problem of dry skin is a reduced production of sebum.
Dryness is a significant problem associated with mature skin as hydration ability progressively decreases and the skin's mechanical properties deteriorate, with loss of suppleness and flexibility.
In addition to these recognised types of skin, many people believe that they have 'sensitive skin'.
Doctors and scientists are not completely agreed about what 'sensitive skin' is, but it may generally be considered as skin which is easily irritated. It is more commonly associated with people with type I skin, and probably has a genetic element.
Some people with this condition cannot tolerate contact with any cosmetic products, however well-formulated they may be.
Sensitive skin can be associated with a medical condition called atopy, where people have an inherited predisposition to eczema, hay fever and asthma. Atopy is discussed further in Chapter 3, 'Some common skin problems'.
Atopic skin. About 15-20% of the population have the genetic ability to develop eczema, asthma and hay fever. The figure has risen considerably in the last few decades.
In several surveys, up to 70% of women said they thought they had 'sensitive skin'.
Truly sensitive or atopic skin may:
- feel very tight after washing
- have a naturally high TEWL rate
- react to many external stimuli by becoming red and blotchy
- be prone to developing dry flaky patches.
Greasy (Oily) Skin
Greasy skin (sometimes called seborrhoeic skin) generally appears at puberty although in a few people it starts much earlier, from the age of six upwards. It is rare after the age of 35. It involves only the upper part of the body, where greater numbers of sebaceous glands are found.
This type of skin is particularly common in adolescents and young adults. At this age there is in both sexes a dramatic increase in sebum production under the influence of the male sex hormones. The extra sebum gives the skin a shiny appearance, especially on the nose and forehead. The epidermis tends to thicken, due to increased keratin production, and the pores dilate. As a result the skin feels rough and irregular.
Mixed skin (often called combination skin) is characterised on the face by thickened, shiny skin associated with patches of dry skin.
Variation with site on the body
Whatever the type of skin, its state and function will differ from one part of the body to another even in the same individual, and will change from time to time. For example, the face, forearms and hands are most exposed to the elements and may suffer from drying and cracking. The bottom is scarcely ever exposed and the skin there is almost always in near-perfect condition. To really see the differences in skin condition in one person, these are the two areas to examine!
Another characteristic that shows considerable variation is the density of the sebaceous glands. There are many more sebaceous glands per unit area of skin in the upper part of the body (forehead >300 per cm²; chest 60 per cm²; upper back 80 per cm²).