A nearly hairless large swollen patch of skin around the genital area of females that becomes very prominent when they are in estrus. These areas swell with fluids and turn bright pink or red due to hormonal changes that occur in preparation for ovulation. The sexual skin also produces odors that excite males of the species. They become highly attentive to the females at this time. Sexual skins are found among many of the Old World monkey species in the subfamily Cercopithecinae (e.g., baboons) as well as the chimpanzees and bonobos.