Sex Differences in Human Thermoregulatory Response to Heat and Cold Stress

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Abstract
The current literature on male-female differences in response to thermal stress has been reviewed. Morphologically, women average 20% smaller body mass, 14% more body fat, 33% less lean body mass, but only 18% less surface area than men. Women have greater body insulation when vasoconstricted (except hands and feet) and a larger peripheral heat sink, but at the cost of (1) greater body fat burden, (2) less muscle mass and strength, and (3) smaller circulating blood volumes which requires greater physiological strain to balance heat production and loss. Under heat stress, women generally show (1) relatively more peripheral blood pooling, (2) greater heart rate increases, (3) more frequent circulatory embarassment, (4) lower maximal sweat rates, (5) higher skin temperatures with greater body heat storage, and (6) poorer maintenance of circulating blood volume with more impact from dehydration. Proportionately fewer women than men can be successfully heat acclimated. In the cold, women generally have (1) less capability for maximum heat production by either exercise or shivering, (2) a more extensively vasoconstricted periphery, (3) lower foot, hand, and mean skin temperatures, (4) greater surface heat losses, especially from the geometrically thinner extremities, (5) increased rates of extremity, but not core, cooling, and (6) relatively greater risk of cold injury.