21 Aug Skin Series part two: how does the skin differ between sex and race?
In part one of the skin series you learnt all about the basic structure of the skin and its role and functions. In part two, I’m going to shed some light on how skin structure can differ between sex and between ethnicity. Everybody’s skin is different and everybody deserves to know how they can look after it best.
So we’ll start with the difference between male and female skin (nb: this article talks about physiological differences in skin of different sexes- this is is no way related to gender and all of the wonderful forms that it takes). The main difference to note is the difference in skin thickness; men literally have thicker skin than women. This is due to the presence of terminal hair follicles as opposed to vellus hair follicles, most importantly on the face. Terminal hair is longer, thicker and darker than vellus hairs, which are much finer, and lighter in colour. It is vellus hair that covers most of the body. This difference in thickness is why men tend to age differently to women (NOT better- love your wrinkles gals). This is as the male beard is made up of terminal hair and this helps the skin to resist wrinkling. The thicker skin is also better at diffusing UV radiation, which causes photo-ageing.
Men also have more collagen in the dermis than women at all ages, although the rates of collagen loss over time are the same in both sexes.
The difference in skin thickness also impacts the frequency of adverse product reactions between the two sexes. The thinner skin of women means that allergens and irritants are more able to penetrate deeper into the skin and thus cause an adverse reaction. However, this increased incidence of adverse reactions in women may also be due to the fact that they tend to use more products than men, thus increasing the chance of coming into contact with an allergen or irritant. Women are also more likely to use products or undergo treatments that damage the skin barrier eg use of micro-dermal abrasion (exfoliation or removal of top layer of skin), or products containing glycolic or lactic acid which are chemical exfoliants. This means allergens or irritants are more likely to penetrate into the skin and cause a reaction.
Another marked difference in skin between sexes is those caused by hormonal differences. After puberty, skin between sexes begins to change differently as the increase in production of both testosterone and oestrogen causes the production of facial and body sebum (oily secretion). This sebum is an ideal food supply for bacteria such as Propionibacterium acnes– the bacteria that causes acne. Testosterone causes an increased amount of sebum production which is why there is typically a higher incidence of acne in men, although females with a higher testosterone level due to hormonal abnormalities such as polycystic ovary disease may experience acne. The higher testosterone levels in men leads to increased rates of production of apocrine sweat (scented sweat produced by specialised glands in the eyelids, breasts, scalp, armpits and genitals) and sebum. As a result, the natural biofilm over the skin in men is different and so adjustments to cosmetic formulations should be made in terms of the skin feel and ensuring adequate hydration levels.
Another huge area where there are marked differences in the skin structure are those dependent on skin colour or racial groups. As mentioned in part one, the colour of the skin is determined by the amount of a pigment present in the skin, known as melanin, which gives the skin brown and some red shades. However, there other pigments that affect skin colour; haemoglobin gives the skin a pink colour, oxyhaemoglobin blueish tones and then carotenoids orange and yellow tones. This difference in skin colour has a number of effects. Firstly and most obviously, darker skin is better protected from the damaging effects of UV rays, and thus those with darker skin tend to exhibit less signs of photo-ageing later on in life (for example wrinkles, thickening of skin and sun spots). Please note, even the darkest of skin can burn, melanin only provides protection equivalent to SPF 7-8!
Another difference in skin of different shades is the response when the skin is damaged or compromised. Post-inflammatory, lighter skin tones do not really show any difference in colour when recovering from injury, whereas darker skin tones often have hyperpigmentation issues. This is because melanocytes (the cells that produce melanin) are considered to be an important part of the immune system, and so the hyperpigmentation is part of the immune response, although the exact reason why is not really known. This should be considered when formulating products for different ethnicities- special care should be taken to avoid any skin irritation to avoid hyperpigmentation issues. However, black skin tones tend to be less sensitive to irritants; white skin tones more commonly show severe reactions. This may be due to the fact that subjects with darker skin tones contain larger mast cell granules– these produce histamine, a compound that is part of the natural immune response.
There is are also slight differences in the structure of the stratum corneum (top layer of skin). Negroid skin has more cell layers than Caucasian skin but the overall thickness is no different- the cells are just packed more compactly. This is going to affect the efficacy of topical treatments or cosmetics as it will reduce how much can penetrate into the epidermis.
Desquamation rates (the rate at which skin is ‘shed’) are also higher in black skin, which affects the ageing process. Asian and black skin tones also have a more compact dermis than white skin. These are likely reasons to the lower incidence of facial wrinkles in Asians and black skin tones.
Black subjects also have bigger and more active sebaceous glands, and so produce more sebum (oily skin secretion) than paler skin tones, and Hispanics have the lowest sebum production. This will affect skin hydration. This has no effect on the incidence of acne- it is similar across all racial groups.
Black and Asian skin tones also have larger and more fibroblasts in the dermis. Fibroblasts are cells that synthesise the main structural elements of the dermis such collagen and the extracellular matrix. This is linked to abnormal scarring- hypertrophic or keloid scarring.
So there really is a biological reason why what may work for your friend, might not work for you. And this isn’t even taking into account more specific genetics, diet, hormones and other factors. The skin is a varying beast not only between individuals, but also varies on the same individual depending on season, diet and just generally over time.
Next up in the skin series…. What causes skin ‘problems’ such as sensitivity or acne? Stay tuned!
Love, The Resident Geek x