Skin of colour and ageing

The process of intrinsic skin ageing involves a progressive decline in tissue function, as seen in many other organs. Contributing factors include cumulative oxidative damage, progressive telomere shortening³ and altered levels of various hormones and growth factors.

Extrinsic ageing and skin of colour

Extrinsic ageing arises predominantly from exposure to ultraviolet light (photodamage), a process, which is superimposed on the background intrinsic ageing of the skin. Exposure to UV light is thought to account for the majority of age-related changes seen in elderly skin, and it has been estimated that up to 80% of facial ageing is attributable to sun exposure.⁴ Clinical features of photoaged skin vary with ethnicity but include laxity, coarseness, increased dryness, altered pigmentation and deep wrinkling.

The changes associated with extrinsic ageing predominantly involve the dermal extracellular components and include massive elastosis, collagen degeneration and alterations to the structure of the collagen and elastin fibre network.⁵

A cross-sectional study by Hillebrand et al6 used image analysis methods to compare the effects of photoageing (on facial skin) in two populations of Japanese females who had lived all of their lives in either Kagoshima (in Southern Japan) or Akita (in Northern Japan); the annual average UVB exposure in Kagoshima being 1.5 times that of Akita. The individuals living in Kagoshima were found to have more numerous and prominent facial wrinkles, more hyperpigmented spots, rougher skin texture and reduced stratum corneum (SC) hydration, thus supporting the ageing effects of cumulative sun exposure.

The process of extrinsic ageing is heavily influenced by the level of skin pigmentation. In the 1970s, Thomas B Fitzpatrick developed the concept of skin phototypes, based on an individual’s skin colour and response to sun exposure (tanning behaviour). The current Fitzpatrick skin type classification can be used to predict skin sensitivity to UV light. Chronic sun exposure in individuals with lightly pigmented skin (phototypes I and II) will produce earlier and more pronounced signs of skin ageing, including atrophy, wrinkling and sagging of facial skin, telangiectasiae and pre-malignant lesions such as actinic keratoses.^7,8

Signs of photodamage are seen in those with more darkly pigmented skin (phototypes IV-VI) but usually occur at a later age and more commonly involve irregular pigmentation or uneven skin tone.⁹ The superior photoprotective qualities of black skin are due to increased melanin content and differences in melanosomal dispersion.¹⁰ The larger, individually dispersed, stage IV melanosomes found in black skin have higher melanin content and are able to absorb more UV light than the smaller, aggregated melanosomes found in Caucasian skin.

A study comparing UV transmission through skin samples from blacks and Caucasians demonstrated epidermal sun protection factors (SPF) of 13.4 and 3.4 respectively, with an average of five times as much UV light reaching the upper dermis of Caucasians as that of blacks.¹¹

A longitudinal study by Hillebrand et al¹² compared the progression of facial wrinkling in different ethnic populations living in the same city over an eight-year period. At the end of the study, the least skin wrinkling and hyperpigmented spots were seen in the East Asian subjects (less than observed in the Hispanic and African American groups). This finding would suggest that individuals from East Asia have mechanisms other than melanin to protect against the effects of UV radiation. Features present at baseline that were found to be predictive of a faster rate of wrinkling included having lighter skin colour and having a drier, more alkaline stratum corneum. Ethnic variation in stratum corneum (SC) structure and function is acknowledged, although there is still much scope for improving our understanding of these differences.

Asian SC is known to have low transepidermal water loss (TEWL), high water content and high lipid (ceramide) levels, however fewer tape strippings are required to disrupt the epidermal barrier (causing increased TEWL) which probably reflects a thinner SC (fewer corneocyte cell layers) and reduced cohesiveness between corneocytes, compared with Negroid skin.¹³

Skin cancer and skin of colour

Important differences in the epidemiology and clinical features of skin cancer exist between ethnic groups. Squamous cell carcinoma (SCC) is the most common cutaneous malignancy in dark-skinned persons, and occurs most commonly on sun-protected sites in blacks suggesting the relative unimportance of UV radiation as an aetiologic factor.¹⁴ 

A review of cutaneous SCC in 163 black patients found commonly involved sites to include the lower extremities and the hair-covered scalp.¹⁵ Melanoma is less common in persons with skin of colour than in Caucasians, however the morbidity and mortality is greater and the clinical features differ.

Dark-skinned ethnic groups tend to develop melanoma on non-sun exposed sites such as the palms, soles and mucosal surfaces (acral lentiginous melanoma) and often present at a later stage with metastatic disease more likely.¹⁶ The most important risk factors for the development of SCC and melanoma in persons with skin of colour are the presence of chronic scarring or inflammatory processes.

It has been suggested that the altered immune function of individuals with darkly pigmented skin (depletion of Langerhans cells) following a single exposure to low-dose UV radiation may confer increased susceptibility to developing cutaneous malignancies, and precautions against sun exposure should therefore be adopted (as is recommended for individuals with lighter skin).¹⁷

Quality of life and ageing skin

The manifestations of ageing skin can significantly impact on the quality of life of older individuals.¹⁸ Chronic exposure to UV radiation contributes to melanocyte ageing and damage, resulting in hyper- and hypo-pigmented lesions. In persons with skin of colour, altered pigmentation is common and depending on various cultural factors can lead to significant psychological sequelae and stigmatisation.

Flat seborrhoeic keratoses are a commonly used indicator of photoageing in Asian skin, with Kwon and colleagues¹⁹ demonstrating an age-associated increase in the incidence of seborrhoeic keratoses in Korean males. Further gender-specific patterns of pigmentary change have been observed in Korean subjects, with lentigines more commonly seen in elderly women.²⁰ 

Melasma is more common in individuals with darker skin types – particularly African Americans, Asians and Hispanics -and can be a sign of photoageing.²¹ Sun exposure is also acknowledged to aggravate this condition.²²

Dermatosis papulosa nigra (DPN)

Dermatosis papulosa nigra (DPN) is an age-related condition and a common cause of cosmetic concern, affecting individuals with black skin and to a lesser extent dark-skinned Asians. DPN lesions are generally best left untreated. Other pigmentary manifestations of photoageing such as idiopathic guttate hypomelanosis and lentigo maligna are seen predominantly in fair-skinned individuals although may occasionally be found in those with darker skin (phototypes IV-VI). In patients with skin of colour it is important to consider other relevant causes of altered pigmentation such as leprosy, vitiligo, leishmaniasis and post-inflammatory lesions.

Evidence from epidemiological studies suggests that tobacco smoke contributes to premature skin ageing, although this occurs to a lesser extent in skin of colour.^23,24 The underlying mechanisms are not fully understood but involve oxidative stress, impaired collagen synthesis and collagen degradation by activated matrix metalloproteinases.²⁵

Dietary intake of fish oils rich in omega-3 polyunsaturated fatty acids is known to confer a photoprotective effect.²⁶ The burdens of comorbidity and polypharmacy increase with age, making systemic disease and drug reactions important considerations in elderly individuals with new skin signs.

Conclusion