4. Expansión urbana del AGEB 2201400583774
6.2. Desarrollo urbano Análisis de CAS, COS y CUS
TOLOGY
:
PRINCIPLES
AND PRACTICE
these data, apocrine glands may be increased in black individuals.
APOCRINE-ECCRINE GLANDS Apocrine- eccrine sweat glands have features of both eccrine and apocrine glands. One study of facial skin reported more numer- ous apocrine-eccrine glands in black skin when compared to white skin.23 SEBACEOUS GLANDSStudies of sebaceous glands and sebaceous gland activity reveal contradictory findings. One study reported increased sebaceous gland size in black patients.95 Another study
reported increased sebum production in black patients.96Three studies indicated
no difference in sebaceous gland activity between black and white subjects.37,97,98
Research in Japanese subjects, however, found a correlation between skin surface lipids and increased pigmentation78(see
Chapter 10).
HAIR Hair composition and structure has been studied between the races. There is no difference in keratin between black and white subjects.99
One study has shown some differences in amino acid composition; however, a follow-up study demonstrated no difference.100,101
Vellus hair follicular density has been studied in African American, Asian, and Caucasian subjects. It has been pro- posed that vellus hair follicles are a potential reservoir for topically applied substances. Vellus follicular hair density was lower in African Americans and Asians when compared to white sub- jects. The authors suggested that this difference may impact skin absorption in different ethnic groups.102
Differences in terminal hair structure between the races have been well stud- ied and are described below.
AFRICAN HAIR In subjects of African descent, four distinct hair types are rec- ognized: straight, wavy, helical, and spiral. The spiral hair type is the most common subtype.103African hair has a
flattened elliptical shape in cross-section with a ribbon-like appearance.104 The
hair is typically coiled tightly, and most naturally shed hairs have a frayed tip. Spontaneous knotting is often seen. Longitudinal splitting, fissures, and breaking of the hair shaft are also observed.105
Other studies of black hair have revealed that black subjects had fewer elastic fibrils anchoring the hair to the dermis.23 This has implications in sev-
eral forms of alopecia frequently seen in
black patients, particularly traction alope- cia. Additionally, there is decreased hair density in African American subjects when compared to white subjects.106 CAUCASIAN HAIRCaucasian hair is typi- cally straight or slightly curved. The hair is elliptical in cross-section. It has the smallest cross-sectional area among eth- nic groups and naturally shed hairs usu- ally have the original or cut tip.104
Spontaneous knotting is rarely observed.105
ASIAN HAIR Asian hair is typically straight. The hair is round in cross- section. It has the largest cross-sectional area and naturally shed hairs usually have original or cut tips.104No sponta-
neous knotting is observed.105
SUMMARY
Understanding the unique characteris- tics of skin of color is extremely impor- tant in cosmetic dermatology. The most well-defined and distinct differences in skin of color pertain to melanin in the skin. Increased melanin in skin of color offers a significant advantage to these patients, namely, a delay in photoaging. The disadvantage of melanin also has great impact in cosmetic dermatology, as this constitutive pigment increases the risk of hyperpigmentation from many cosmetic procedures.
Apparent differences in fibroblasts in skin of color also greatly impact the practice of cosmetic dermatology. These fibroblast differences likely place patients with skin of color at increased risk of hypertrophic scars and keloids after invasive surgical and laser proce- dures.
More than half of the world’s popula- tion has skin of color. Despite this fact, our understanding of skin structure and function is limited in these patients. Research to date has been quite com- pelling; however, most research on skin of color is preliminary. Further research and larger population studies are neces- sary to definitively describe the similari- ties and differences in skin structure and function among the various ethnic groups.
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