 |
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.
