Exploring Hyperpigmentation in Skin of Colour

Hyperpigmentation is defined as darkening patches of skin.

This occurs when the skin produces more melanin; the pigment that gives skin its colour. Although hyperpigmentation occurs in all skin types, it is one of the main skin complaints of people with darker skin tones. Facial hyperpigmentation can cause significant cosmetic disfigurement with subsequent emotional impact.^1,2,3
Darker skin types are generally classified as Fitzpatrick types IV-VI. There are structural and functional differences in the skin, which produces variances in skin conditions, presentation and treatments. These skin types are categorised by higher melanin content and more effective distribution of melanin, producing better protection against ultraviolet (UV) radiation. Melanin is generally classified into two types: eumelanin and pheomelanin. Darker skin types have a higher eumelanin to pheomelanin ratio, and higher amount of eumelanin than lighter-skinned individuals.⁴ 

The concentration of melanin in melanosomes within the epidermis is double in those with darker skin compared to lighter-pigmented individuals, although the number of melanocytes is the same. There is also a slower degradation of the melanosome within a keratinocyte in individuals with darker skin. These structural and functional differences mean special considerations need to be given when diagnosing and treating skin of colour.⁵ 

The process of melanin production 

The process of melanin production is regulated by the enzyme tyrosinase. This enzyme converts L-tyrosine L-3,4-dihydroxyphenylalanine (L-DOPA), which is then oxidised to form L-dopauinone. This key compound can then follow two different pathways depending on the availability of cysteine to form eumelanin or pheomelanin (Figure 1).^6,7
Melanocytes are cells within the basal layer of the epidermis responsible for producing melanin. Once formed, melanin is then packaged into small, round organelles called melanosomes which are transported to neighbouring keratinocytes via dendritic processes. They are deposited superficially to the cell nucleus to offer protection from UV radiation (Figure 1).⁸ 

When this process goes into overdrive, excess melanin is produced and can cause darkening of the skin in that area. This is known as hyperpigmentation and occurs in various forms, which happen all over the body in small patches, spots or larger areas. There are many reasons why this happens, which are discussed next. 

Sun damage 

This is the main cause of hyperpigmentation and can exacerbate existing hyperpigmentation. The initial melanin production from sun exposure acts as a natural sunscreen to protect from harmful UV rays. However, excess UVA and UVB exposure disrupts the melanin production, which leads to increased pigmentation. This pigmentation can be harder to treat as it is produced in the dermal layers of the skin. In fact, this result can happen from any UVA and UVB source, including sunbeds.⁵ Sun damage induced hyperpigmentation can present in multiple ways. Most commonly as ‘sunspots’, also known as ephelides and lentigines which presents as tan-dark brown macules or patches. Another presentation is melasma, which has multiple causes, one of which is intense sun exposure. This is visible as symmetrical light to dark brown patches with irregular borders and is most commonly seen on centrofacial, malar and mandibular regions. Many of our mature skin-of-colour patients will experience darkening of malar cheeks and the forehead which is diagnosed as maturational dyschromia and has developed from years of chronic sun exposure. A rare presentation of sun induced hyperpigmentation is Lichen planus pigmentosus which favours Fitzpatrick lll-V skin types. It presents on sun-exposed areas as grey-brown to brown macules and its distribution indicates UV radiation as the cause.⁵ 

Hormones 

It has been shown in a number of studies from across the world that increased levels of oestrogen constitute a risk factor for hyperpigmentation disorders.⁹ This change in oestrogen levels is commonly seen in pregnancy. When hyperpigmentation presents in this way it is known as the mask of pregnancy – a form of melasma. As mentioned above melasma has multiple causes. Fortunately, in most cases it resolves or fades itself after pregnancy, however it can reappear with exposure to UV rays.⁵ These hyperpigmentation changes can also be seen with hormone replacement therapy (HRT) and combined oral contraceptive pills. Due to the decrease of oestrogen in menopause, it has been shown to improve symptoms of melasma when not taking HRT.⁹ 

Skin injuries and inflammation 

This is the main cause for post-inflammatory hyperpigmentation (PIH).¹⁰ Injuries such as cuts, burns, chemical exposure, infections or inflammation can lead to darkened patchy skin. Incorrect skin treatments which lead to damage and inflammation can also cause PIH. The long-term application and misuse of skin-lightening agents containing hydroquinone can lead to the formation of a blue-black pigmentation known as exogenous ochronosis. It is therefore important that prescription topical formulations of hydroquinone are used under clinician supervision.⁵ Allergens in cosmetics or textiles can induce pigmentated contact dermatitis also known as Riehl’s melanosis, which is characterised by a brown-grey appearance on areas of application.⁵ 

Genetics 

Hyperpigmentation can also be a hereditary condition seen more commonly in darker-skinned patients. This typically presents itself as a brown-black pigmented area around the eyes, known as periorbital hyperpigmentation.⁵ 

Illnesses and medication 

Systemic conditions such as Addison’s disease and hyperthyroidism cause a diffuse hyperpigmentation. It tends to be more pronounced in areas of sun exposure. Hemochromatosis, a disorder of iron storage and deposition, causes a slate-grey hyperpigmentation.¹¹ Acanthosis nigricans typically affects Fitzpatrick Vl skin types and presents as thickened, hyperpigmented plaques. This is commonly associated with insulin resistance, obesity and polycystic ovary syndrome.⁵ A range of medications from chemotherapy drugs to antimalarials and anti-epileptic medication can also cause grey patches of pigmentation.¹² 

Prevention 

Educating and advising patients about sun protection is key in preventing hyperpigmentation in the first place. It is important patients understand that sun protection needs to be used 365 days a year and that the sun will cause damage even on cloudy days.¹² A broad-spectrum SPF 30+ needs to be used daily to give adequate protection from UVA and UVB rays.13 Many sunscreens now come in tinted formulations to help camouflage pigmentation too.⁵ 

To help prevent hyperpigmentation, patients should:^5,14 

• Avoid peak hours of sunlight between 11am to 3pm when the sun’s UV rays are at their strongest 
• Seek shade and wear protective clothing such as sun hats and sunglasses 
• Use sun protection daily 
• Avoid picking or scratching spots or scabs 
• Avoid products or treatments that will cause irritation and inflammation of the skin 

When it comes to treating pigmentation, it is important to first identify and eliminate the cause. A tailored skincare regime can then be developed which suits the patient’s skin type and condition. This can help reduce the appearance of pigmentation and also prevent it from forming. It is important to note here that treatment of hyperpigmentation can be a difficult and prolonged process. There have been better results seen with epidermal pigmentation compared to dermal pigmentation and the patient needs to be informed and have their expectations managed.

Topical treatments 

Hydroquinone 

This is considered the gold standard and most effective topical agent for treatment of pigmentation. Its mechanism of action is to inhibit tyrosinase and, in turn, the conversion of L-DOPA to melanin.¹³ Hydroquinone should be used with caution and for limited periods of time because if misused or used excessively it can lead to erythema, irritation, confetti-like depigmentation with higher concentrations, and exogenous ochronosis.⁵ 

Retinoids 

These are a form of vitamin A. Common preparations are retinoic acid, tretinoin, adapalene and tazarotene. They work to reduce hyperpigmentation through multiple mechanisms: increasing cell turnover, reducing melanin transfer via melanosomes, and allowing increased penetration of other active ingredients 

Ascorbic acid 

Ascorbic acid, also known as vitamin C, decreases melanin production by interacting with copper ions at the tyrosinase-active site, which inhibits the action of the enzyme tyrosinase.¹⁷ Vitamin C is a powerful antioxidant and further reduces hyperpigmentation with its photoprotective properties. 

Niacinamide 

Niacinamide reduces pigmentation by reversibly preventing the transfer of melanosomes from melanocytes to the keratinocytes. It is an important component of many over-the-counter lightening creams.²⁰ 

Kojic acid 

This is a naturally-occurring fungal product derived from certain species of acetobacter, aspergillus and penicillium. It works by reducing the production of free tyrosinase and as a powerful antioxidant.²¹ 

Liquorice derivatives 

Liquorice is a root extract from glycyrrhiza glabra. It has many important properties such as anti-inflammatory, antiviral, antimicrobial, and anti-carcinogenic.²² It contains two active ingredients – glabridin which inhibits tyrosinase and possesses anti-inflammatory effects^23,24 and liquitrin, which causes melanin dispersion and removal.²⁵ 

Azelaic acid 

This was initially developed as an anti-acne agent but was also found to have inhibitory effects on tyrosinase. Its use has now been extended to hyperpigmentary disorders such as melasma and PIH.²⁶ 

Cysteamine 

This is a newer ingredient on the market that has promising outcomes. It has been shown that topical cysteamine 5% has considerable results in treating stubborn hyperpigmentation in ethnic populations.^27,28 It also induces fewer side effects to other topical agents. 

Many of these topical ingredients can be used in isolation or more commonly in combination. Topical agents work on different stages of melanogenesis so, when combined, can give better therapeutic results. 

 When it comes to treating pigmentation, it is important to first identify and eliminate the cause. A tailored skincare regime can then be developed which suits the patient’s skin type and condition  

Physical treatments 

Chemical peels 

These are common procedures for reducing hyperpigmentation and can be used alone or combined with other modalities. For patients of a darker skin tone, it is best to be cautious and limit to superficial peels only, as medium and deep peels may be more likely to cause further irritation and pigmentation.⁵ A superficial peel combined with regular topical therapy can produce better results than chemical peels alone.^10,16 

Laser 

Laser therapy can be an effective treatment for hyperpigmentation. However, this modality needs to be used cautiously in darker-skinned patients due to the higher melanin content. Melanin has a broad absorption range which unfortunately means that lasers targeted for the deeper dermal melanin can be absorbed by more superficial epidermal melanin leading to further pigmentation, blistering and scarring.^29,30 

Hyperpigmentation treatment with lasers has been associated with an unpredictable response, frequent relapses and high risk of both post-inflammatory hyper- and hypopigmentation.²⁹ It is advisable that only experienced practitioners carry out this treatment and patients should be counselled about the side effects and results that can be achieved. 

Microneedling 

There are various studies to show that microneedling is a popular option for treating pigmentation in darker-skinned individuals, in particular, melasma and periorbital pigmentation.^31,32 The microchannels produced during treatment not only induce collagen production, but also improve the transdermal drug absorption compared to topical treatments alone.^33,34 

Dermabrasion 

A study from 2001 showed that in a mixed Fitzpatrick skin type group, dermabrasion produced successful results on more resistant melasma or dermal pigmentation.³⁶ However, due to the depth of treatment it should be used with caution on darker-skinned patients as there is a higher risk of developing prolonged erythema, hyper/ hypopigmentation and hypertrophic scarring.³⁷ Microdermabrasion on the other hand, is less invasive with reduced downtime and therefore less risks.³⁹ 

Conclusion 

The UK has a diverse population with the skin of colour proportion growing steadily. Hyperpigmentation is prevalent within this group and we are therefore more likely to treat this skin concern. As discussed in this review we have a challenge to correctly diagnose, effectively counsel and provide consistently successful treatments to all our patients. There are a number of ways to treat hyperpigmentation, but with varying degrees of success. It is important to select the correct treatment based on the patient’s skin type to prevent any further damage and manage expectations. Hyperpigmentation is a distressing condition and we have the ability to help these patients improve their concern and quality of life