Types of skin
The Skin has two layers.
These are the Epidermis (top layer) and the Dermis ( deep layer).
The Skin and how it Works
There are four major layers of keratinocytes (the structural cells) in the epidermis.
1. The Stratum basale, has cells that are shaped like columns.This is the deepest layer. In this layer the cells divide and push cells into higher layers.Therefore this layer is the provider of all cells of the epidermis. As cells move into the higher layers, they flatten and eventually die. This results in constant renewing epidermal cells.
2. The Spinosum layer is the next layer, where the cells start to synthesize keratin.
3. The Stratum granulosum, layer cells are dead, as they have lost their nuclei. Keratin proteins & water-proofing lipids are produced here.
4. Stratum corneum This is the outermost layer made up of 25-30 layers of dead keratin and forms the protective barrier of skin.
The Stratum corneum cells are responsible for maintaining the integrity and hydration of the skin by acting as a barrier that allows the body to be separated from the environment thereby preventing toxins, bacteria and poisons from entry into the organism &preventing water loss.
DEFINING DARK SKIN OR ‘SKIN OF COLOUR’
Dark/black/ethnic skin or ‘skin of colour’ are some terms that refer to the broad range of skin types and complexions in people with highly pigmented skin. Often these labels are given to people of Asian, African, Hispanic, Native American, Caribbean or Middle Eastern descent. All of these races and ethnicities have many differences and therefore their skins can be very different too although the label of ‘dark skin’ often applies broadly to them all.
- Caucasoid (Europeans, Middle Easterners, Indians, Pakistanis)
- Mongoloid (Asians: East Asians, Indonesians, Polynesians, American Indians and Eskimos).
- Australoid (Australian Aborigines)
- Congoid (Africans and descendants of Africa such as African Caribbean)
- Capoid (A specific tribe of Africa)
In the modern world, this classification system is practically obsolete due to migration and changes in geographical placement. Racial classification is not helpful in Dermatology because skins of very different tones can exist in the same Racial group.
A person’s ethnicity is based on heritage, language, culture, and national origin and often skin colour.
It is a social construct that is poorly defined and the concept of someone’s ethnicity can often be difficult to identify or specify.
As opposed to the term, ‘race’, ‘ethnicity’ classifies individuals and populations on the basis of shared social variables, such as religion, customs and language and not just geographical positioning and skin colour.
Race & Ethnicity are widely interchangeable or used as an all-inclusive label.
Categorisation of race and ethnicity is a social construct and not a scientific method of classification.
It is more useful to group individuals who share common skin and hair characteristics as well as geographical and cultural similarities.
WHAT IS CLASSIFIED AS ‘DARK SKIN’?
The dark-skinned population is very widely geographically spread around the world. Dark-skinned people are most commonly, but not only, from North, Central and South America, Africa, Asia and the Middle East. Due to rises in immigration, there are now also a large number of dark-skinned people all around Europe too.
In the context of dermatology, it is increasingly important to recognize clinical and cultural differences in dark-skinned patients, keeping these demographic trends in mind.
As dark-skinned people make up such a significant part of the global population, the prevalence of specific approaches, treatments and procedures for dark skin is of great importance.
THE FITZPATRICK SKIN PHOTO-TYPE (SPT) SYSTEM
This is a classification system, which was originally set up in 1975 on the basis of an individual’s sensitivity to sunlight. In other words, it is intended to classify a person’s response to UV radiation, how badly someone burns or how well someone tans. It therefore tries to exclude the confusion caused by using Race or Ethnicity.
|SKIN TYPE||APPEARANCE||REACTION TO SUN EXPOSURE|
|TYPE I||Very fair; blond/light or red hair, blue/green/light coloured eyes, often freckles present on skin||Always burns,
|TYPE II||Fair skin, light coloured hair and eyes,||Burns easily,
|TYPE III||Probably the most common skin type; fair skin, eye and hair colour varies||Always tans,
|TYPE IV||Mediterranean or ‘olive’ Caucasian skin||Always tans,
|TYPE V||Brown or Middle Eastern skin, rarely sensitive to sun||Always tans,
|TYPE VI||Black/dark brown skin, rarely sun-sensitive||Never burns,
However, the SPT system is not very concise because there as so many variables within racial groups and skin types.One SPT type can consist of many varieties and levels of skin colour
Dry Skin: This occurs when the epidermis of the skin does not contain enough lipids; therefore not enough moisture is kept in the skin. This can be due to internal factors, such as stress, illness, drug therapy or hereditary disposition of dry skin. It can also be due to external factors, such as weather and cleansers.
Oily or greasy skin: Sebum is the skin’s protective mantle, which helps to keep the skin supple. Excess sebum production causes oily skin, which can lead to the formation of spots, black heads and pimples.
Combination skin: This is when the nose, forehead and chin are oily (the T-Zone), due to more sebaceous glands being present there, while the cheeks are dry.
Sensitive skin: This is usually very dry and reacts to many external substances, causing red, itchy, blotchy, flaky skin.
Hyper-pigmented skin: The skin looks patchy due to excessive melanin in some areas.
Wrinkled Skin: Loss of sub-dermal fat (i.e under the skin) causes larger wrinkles & sagging at rest. Fine wrinkles are due to loss of collagen & hyaluronic acid in the dermis.
WHAT DEFINES SKIN COLOUR?
Melanin: The major aspect determining the colour of the skin is a pigment called melanin, which is present in packets called melanosomes, which are found within specialised cells known as melanocytes, that are present in the skin’s cell producing layer (also known as the basal layer).
There are two types of melanin in the human body:
- Eumelanin (black) &
- Pheomelanin (red),
The natural colour of the skin depends on the amount of and the balance between these two types of melanin.
Blood circulating (Haemoglobin) through the tiny capillaries close to the surface.
Carotene, a yellowish pigment, which is found in varying quantities throughout the layers of the skin.
The melanocytes in dark skin, although physically bigger are present in the same quantity as Caucasian (pale ) skins, are genetically programmed to produce more melanin.
There is also a difference in the character of the melanin produced, as the melanosomes in coloured skins are larger and individually dispersed throughout the skins layers compared to the smaller and more concentrated melanosomes found in lighter skin.
Melanin protects the skin against sunburn and helps prevent the development of skin cancers by absorbing ultraviolet radiation.
However, even though dark skin absorbs much more solar radiation than Caucasian skin, there is a lower incidence of sun-induced skin cancer.
ASIAN & DARKER SKIN CHARACTERISTICS
(SKIN PHOTO-TYPES 3-5)
Asian & darker skins:
- Have larger, more numerous sebaceous glands, denser epidermis and larger melanin cells compared to Caucasian skin.
- They are more prone to noticeable scarring.
Products especially effective at fading scars are those, which contain a combination of Vitamins A, C and E with silicones, which, promotes normal skin repair and rejuvenates the skin.
- Easily darkened by the sun.
Their skins have larger melanocytes compared to Caucasian skin, therefore able to produce Melanin very quickly and darkening much faster. To prevent this from happening, products with a high SPF factor (of 25 or more) used as a daily moisturiser, is recommended for dark skins.
Therefore sun protection is essential for both light and dark skins. It prevents dark patches in dark skins, and wrinkles in fair skins.
- Acne is a more frequent problem in dark skins, due to the higher numbers of sebaceous glands releasing sebum. If it is not dealt with properly, visible scarring and darker pigmented areas can cover the face, which can be very distressing.
STRUCTURAL AND FUNCTIONAL DIFFERENCES IN DARK SKIN
There are fundamental differences between dark coloured skin and Caucasian (white) skin that go beyond the obvious aesthetic difference.
In addition to the different character and quantity of melanin in dark skin, there are also differences in the structure of the stratum corneum (outer layer) and its water retaining abilities.
The belief that a coloured skin is more resilient than white skin is often incorrect, as dark skin is commonly sensitive, but concealed by the deeper pigmentation.
EPIDERMAL STRUCTURE & FUNCTION
This is the outermost layer of the skin There are believed to be some differences between light and dark skin concerning the stratum corneum. Although black and white skin is usually of equal thickness, black skin may contain more cell layers.
Therefore this layer in dark skins is denser. Black skin is also considered to have increased spontaneous desquamation (the shedding of the outermost layer of the skin) compared with white and Asian skin. The more compact stratum corneum in dark skin may influence the effectiveness of topical therapies or cosmetic processes such as chemical peels.
BARRIER FUNCTION: The epidermal barrier provides an effective covering that stops the unnecessary loss of body fluids and also controls the absorption of infectious or toxic substances that come from outside the skin. Trans-epidermal water loss (TEWL) is the amount of water vapour lost from the skin, (not taking sweat into consideration.)
LIPID CONTENT: It is generally considered that dark skin has a higher lipid content that light skin. Lipid levels can significantly influence the epidermal water content and therefore should be an important variable in evaluating which topical cosmetic and pharmaceutical agents are right for a particular skin tone.
DERMAL STRUCTURE & FUNCTION
There are very few dermal differences between light and dark skin. The only significant changes are due to chronological ageing and photo-ageing.
FIBROBLASTS AND BLOOD VESSELS: Black skin tends to have numerous and large fibroblasts (the cells in the skin which produce collagen) whereas, white skin tends to have less. This heightened activity of fibroblasts can lead to keloid and hypertrophic scar formation, conditions which are common in black skin. Likewise, black skin usually has more numerous superficial blood vessels than white skin.
A keloid scar can develop after an injury has healed, such as a cut, burn or an acne lesion. It develops because there is an overgrowth of dense fibrous tissues and a build up of collagen in one particular area which produces a lump, often much larger than an original scar.
People with dark skin may have a greater tendency to develop keloid scarring; as they have an increased number and size of fibroblasts, the cells in the skin which produce collagen.
This can lead to a build up of collagen and develop a keloid or hypertrophic (raised) scar.
INGROWN HAIR/ RAZOR BUMPS
(PSEUDOFOLLICULITIS BARBAE (PFB)
People of African descent often have cosmetic problems with ingrown hairs or razor bumps. Because the hair shafts are curly, the hairs that come out are quite tightly coiled. After shaving, the curly hair can be cut into a sharp point and if aimed back towards the body rather than outwards, it can grow back into the skin. The immune system sees these inwards-growing hairs as “invaders” from the outside, which is attacking the body. This reaction develops bumps, or inflammatory lesions on the skin.
Women with dark skin who tweeze or pluck their facial hair will find that the hair breaks below the surface of the skin, pierces the hair follicle and then produces the same inflammatory response and bumps.
Fortunately, there are also several hair removal methods and treatments available for both men and women with PFB.
WATER RETAINING ABILITY
There are many misconceptions about dark skin; one of them is that darker skin is thicker and tougher than white skin.
The thickness of dark and light skin is the same, although there is evidence that the stratum corneum (outer layer) of dark-coloured skins contains cell layers that are more compact than in Caucasian skins. There is a direct relationship between these compact layers and the skins ability to retain water.
In the skin there is a process, which is known as transdermal water flow. This water flow begins at the basal layer and moves up through the skin layers and onto the surface, where it eventually mixes with the secretions from the sweat glands in the hair follicles. At the surface, the water portion of this mixture evaporates and helps cool the body. The speed of this water flow through the skin and the outer layers ability to retain that water will ultimately determine the moisture level and dryness of the surface.
In darker skin, the increased density of the outer layer also affects the lipids (skin oils) that are found in the spaces between the skin cells, as they are also densely compacted. This compacting of these lipids makes the dark skin more permeable to water. These factors result in a higher flow and subsequent loss of water from dark skins than that of Caucasian.
Consequently, dark skin, because of the higher transdermal water flows, will have a tendency to suffer from dryness unless steps to retain the available moisture are taken.
As dark skin has a tendency to get too dry, it will be common for it to also experience a high degree of sensitivity, and because sensitivity is harder to detect in a coloured skin by the untrained eye, it is often overlooked as a cause of irritation.
Quite often, redness (erythema) of the skin, caused by contact with sensitising substances will often remain in a coloured skin longer than that of a Caucasian skin. Depending on the base colour of the skin and the type of the sensitizer, erythema can be seen on coloured skin as a deepening grey to purple stain, lasting as long as 24 hours after contact. The toleration of cosmetic products designed for fairer, Caucasian skin may be lower on a coloured skin because of the tendency to sensitivity, and special care may be required to avoid irritating or adverse reactions
Photo-damage results from the long-term effects of exposure to the sun. It is clinically categorized by:
- Dark spots
- Droopy skin
- A yellowish tint
- Broken blood vessels
- Leathery skin
- Skin cancers
As we age, our skin becomes less efficient in producing new skin cells, which makes it look thinner and feel rougher.
Over time, we tend to damage the basic structure of our skin due to several factors, which means it will not completely recover from long-term harm.
Even though the epidermis will still be able to regenerate itself, the dermis will not & some scarring will always remain.
The skin is constantly being damaged by UVA & UVB light from the sun, as the structure of the cell layers gradually deteriorates. With constant exposure to the sun, the supporting collagen & elastin fibres in the dermis also get damaged, leading to fine wrinkles.
The visible ageing process is not only due to the skin damage, but also because of the under-lying muscles becoming weaker, resulting in the skin being pulled out of shape.
Photo-ageing affects all races and skin types.
The signs of photo-damage can appear at an early age, such as in individuals who have freckles because of UV exposure.
However, there are some clinical differences between lighter and darker skin types and their responses to photo-damage.
In lighter skin types, signs of photo-damage include wrinkles, loss in elasticity, sallowness and discolouration. Pre-malignant or malignant skin lesions, such as actinic keratoses, can also accompany these features. Actinic keratosis is a premalignant skin condition where thick, scaly, or crusty patches appear. It is more common in fair-skinned people than in darker skin. Some of these pre-cancers can progress into squamous cell carcinoma (a form of cancer), and therefore they should be treated as soon as possible.
These lesions may appear on any area of the skin, which is frequently exposed, to the sun, such as the face, ears, neck, scalp, chest, backs of hands, forearms, or lips.
In deeply pigmented skin, photo-damage may be recognised in the forms of mottled facial pigmentation, rough texture and fine wrinkles. Severe photo-damage such as pre-malignant or malignant lesions are uncommon in dark skin, particularly in people of African descent.
Overall, compared with light skin, black skin shows very little evidence of sun damage.
Some black-skinned individuals may be affects by Dermatosis papulosa nigra, the presence of multiple, smooth, firm, black or dark brown papules, which most commonly appear on face and neck.
Skin types 3-6 (darker skins) tend to develop mottled-pigmentation and thicker, deeper wrinkles on the forehead, around the mouth and in the ‘crow’s feet’ area compared to Caucasian skin.
Asian skin may also develop seborrheic keratoses due to photo-damage. These are very common, benign growths which can appear anywhere on the body. They are not malignant, although some malignant lesions may resemble seborrheic keratosis.
They usually start as light-brown, even skin-coloured, flat areas, which vary in size but are usually quite small. They grow thicker and rise above the skin surface and can become dark brown or almost black with a ‘stuck on’ appearance. They may be smooth or rough.