PREGNANCY is normally associated with a deposition of pigment in characteristic areas already pigmented. Thus the nipples and areolae, the linea alba, the vulva, the navel and the face slowly accumulate pigment during gestation. The pigmentary response to pregnancy varies in different individuals. Brunettes show a greater response than do blondes. A Japanese, Nishizaki, suggested that the degree of pigmentation is an excellent index of the general physical response to the stimulation of pregnancy. In a few individuals, the increased pigmentation of the face involving the cheeks, the forehead, and the bridge of the nose presents a characteristic picture.which has been designated as the “mask of pregnancy,” or chloasma gravidarum. These areas of increased pigmentation gradually lose their excessive pigment and slowly fade out after the patient's delivery. In recent years the pigmentary response of pregnancy has been regarded as endocrinal in origin. The first experimental evidence for melanin formation in the mammalian skin by hormonal action was presented by Lipschiitz in 1930. This author transplanted ovaries into kidneys of castrated male guinea pigs and observed considerable pigmentation around the nipples after the operation. Similar results were obtained by Bloch and Schrafl in castrated male guinea pigs after the injection of estrogens. These experiments definitely involved the female gonad in the mechanism of pigmentation.
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Davis et al. (1945) studied this question.