Heat intolerance as a function of percent of body surface involved with miliaria rubra

Twenty-four heat-acclimatized male volunteers were wrapped as previously described (Am. J. Physiol. 239 (Regulatory Integrative Comp. Physiol. 8): R226-R232, 1980) but to produce miliaria rubra (heat rash) in specific regions of the body. Three experimental rash groups were involved: 1) the torso (17% total skin surface rashed, n = 6), 2) torso and arms (38%, n = 8), or 3) legs (41%, n = 6), while four subjects served as controls. All subjects were reexposed to walking in the heat on the 7th day after unwrapping, and again 14, 21, and 28 days after unwrapping. When compared to responses for the last heat acclimatization day, tolerance time and sweat rate were lower and mean body temperature and delta heat storage significantly higher for experimental rash subjects contrasted to the controls for up to 21 days; however, no significant differences between the three rashed groups were found. The critical amount of surface area for heat intolerance from heat rash appears to be related to the specific region of the body and associated sweating responses; smaller rashed areas of the trunk, because they have greater potential for abundant sweating, may produce similar responses to heat stress as larger rashed areas of the limbs. Heat intolerance due to rash was not resolved until after 21 days.