Definition of race

The characteristics of our species, Homo sapiens, are continuously variable, and hence the division into ‘races’ is – to some extent – artificial. However, there are obvious differences between groups of humans, and these differences have an influence on the appearance of and susceptibility to disease. Most definitions of a ‘race’ are unsatisfactory, but perhaps the best is ‘a population that differs significantly from other populations in regard to the frequency of one or more of the genes that it possesses’. Obviously, this definition allows even rather small groups to be classified as a race!

It is generally assumed that changes in gene frequency result from mutation, natural selection and ‘accidental’ loss. Some changes are thought to be the result of adaptation to environmental conditions, although it is not always obvious what advantage is conferred. Racial classification has relied on physical characteristics, often skeletal, although hair form and skin colour are taken into account. The main divisions are the following:

Racial differences in normal skin

The most obvious difference is in pigmentation (p. 74), but hair forms and colour also vary. Mongoloid hair is straight and has the largest diameter; black African hair is short, spiralled, drier and more brittle than that of other races; and caucasoid hair may be wavy, straight or helical. Hair colour is predominantly black in mongoloids and Africans, and black, blond or red in caucasoids. Body hair is most profuse in caucasoids. The black African stratum corneum differs from that of the caucasoid by showing greater intercellular adhesion and a higher lipid content.

Diseases that show racially dependent variations

In pigmented skin, eruptions that appear red or brown in white caucasoid skin may be black, grey or purple, and pigmentation can mask an erythematous reaction. Inflammation in pigmented skin often provokes a hyperpigmentary (Figs 1 and 2) or hypopigmentary (Table 1) reaction. Follicular, papular and annular patterns are more common in pigmented skin than in caucasoid. In addition, some skin disorders show an inter-racial variation in prevalence (Table 2).

Fig. 1 Lichen simplex chronicus showing hyperpigmentation and lichenification.

Fig. 2

Buy Membership for Dermatology Category to continue reading. Learn more here