NUNNELEY, SARAH A. Physiological Responses of women to thermal stress: a review. Med. Sci. Sports. Vol. 10, No. 4, pp. 250-255, 1978. The recent increase in women's participation in physically challenging activities prompted this review of female responses to heat and cold (68 references). Relevant sex differences include hormone levels, anthropometric factors, and body composition. Many studies show that women are less heat tolerant than men, particularly when physical work is required. Much of the difference is related to women's relatively low level of physical fitness and lack of heat acclimatization, which are in turn a result of their traditionally sedentary lifestyle. When work load is adjusted relative to individual capacity, females respond to heat stress much as males do. Acclimatization mechanisms are the same. Women generally have lower sweat rates, an appropriate adjustment to lesser cooling needs. The menstrual cycle has no meaningful effect on heat tolerance. Cold response reflects individual subcutaneous fat thickness, and women have an advantage there, but in extreme cold exposure they may be handicapped by their small muscle mass. Sex per se is but a small factor in determining human thermal responses; individual body size, physical fitness, and state of acclimatization play far more important roles.