|
Figs. 3.5a,b. An African
American women who appears
younger that a Caucasian women
of the same age |
It is well established that melanin confers protection from UV light. Kaidbey demonstrated increased photoprotection by melanin in black compared with white skin [29]. The mean protective factor for UVB for black epidermis was 13.4 compared with 3.4 for white epidermis. Similarly, the mean protective factor for UVA for black epidermis was 5.7 compared with only 1.8 for white epidermis. Given the photoprotective effect of melanin, one would anticipate that African Americans would display fewer changes associated with photoaging compared with those individuals with white skin. Hence, African American women often appear younger that Caucasian women of the same age (Fig. 3.5a,b).Additionally, the onset of the cutaneous manifestations of photoaging reportedly occurs at a later age in African Americans compared with whites [30]. As would be expected, photoaging in African Americans in more pronounced in individuals with lighter skin hues [31]. Long-term sun exposure to African American skin does not produce the readily apparent characteristics of photoaging observed in white skin. For example, wrinkling beside the lateral canthi of the eyes and at the corners of the mouth occurs less often in African Americans compared with whites [32]. Montagna also found that shrinkage and reduction of dermal volume leading to sagging of the facial skin occurred less precipitously in the facial skin of young and middle-aged black women.
Photoaging features most often apparent in the African American population include fine wrinkling, skin textural changes, benign cutaneous growths, and pigmentary abnormalities [33]. Although not well characterized, there are several pigmentary abnormalities observed in African American skin.Hyperpigmentation assumes several forms. Focal areas of hyperpigmentation, either mottled or more confluent, impart an uneven skin tone,which is a common cosmetic complaint for African America women in particular (Fig. 3.6). Another not uncommonly observed type of
|
Fig. 3.7. A generalized darkening
of the facial skin compared with
the sun-protected areas of the
upper chest and shoulders in this
African American woman |
hyperpigmentation is a generalized darkening of the facial skin compared with the sun-protected areas (Fig. 3.7). It is known that skin pigmentation
|
Fig. 3.6. Focal areas of
hyperpigmentation, either mottled
or confluent, impart an uneven
skin tone to the faces of many
African America women |
increases with exposure to both UVA and UVB radiation. Whereas the production of melanin from the stimulation of UVB is of short duration, that due to cumulative UVA exposure appears to be much longer lasting [34]. UVB-induced pigmentation disappears with epidermal turnover within a month, in contrast to UVA pigmentation that may last several months to a year. The difference is likely related to the basal localization of UVA-induced pigment. Long-term UVA-stimulated pigmentation may very well explain the general darkening of the sun-exposed skin frequently observed in African Americans.
Solar lentigines are not a primary component of photoaging in African American skin. This is undoubtedly related to the photoprotective effect of melanin, as discussed previously. Although not formally studied as in Asian skin, it has been observed that benign pigmented lesions are a frequent component of aging in African Americas. Seborrheic keratoses are noted on sun-exposed as well as sun-protected skin. Dermatosis papulosa nigra (DPN), a type of seborrheic keratosis, is prominent only on the sun-exposed facial skin of both African American men and women. It is theorized that chronological aging and cumulative sun exposure are variables for the development of DPNs.
Disorders of hypomelanosis are readily apparent in African Americans, given the contrast between the normally pigmented skin and the contrasting white area. Guttate hypomelanosis is characterized by multiple, small, depigmented macules on the anterior surface of the legs, lower abdomen, and arms [35]. The macules are circular with well-defined borders. The differential diagnosis in this group would include vitiligo.
In summary, in African American skin, discrete and confluent hyperpigmentation, seborrheic keratoses, dermatosis papulosa nigra, and idiopathic guttate hypomelanosis are the major pigmentary alterations demonstrated.
