The influence of ethnic differences upon human responses due to thermal environment

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  • J. therm. Biol. Vol. 18, No. 5/6, pp. 285-287, 1993 0306-4565/93 $6.00 + 0.00 Printed in Great Britain. All rights reserved Copyright 1993 Pergamon Press Ltd





    IDepartment of Regional Planning, Toyohashi University of Technology, Tenpaku Toyohashi, Aichi Prefecture 441, 2Department of Architecture, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya

    466, Japan

    Al~tract--l. The influence of ethnic differences is discussed with reference to the following issues. 2. It has been found that total numbers of active sweat glands increase in tropical populations compared

    with people from northern latitudes. 3. It has also been observed that the active sweat glands of Eskimos are fewer than those of Caucasians. 4. The rate of the evaporated sweat loss was calculated by measuring body weight loss and it

    was found that the evaporated sweat loss of Caucasians is larger than that of Japanese in the same climate.

    5. Meteorological factors might have been responsible for the smaller loss in Japanese compared with that of Japanese-Americans.

    6. Under the same experimental conditions, it was observed that there were little or no differences between the Caucasians and Negros.

    Key Word Index: Ethnic difference; evaporated sweat loss; sweat gland density; therman stress; required sweat rate.


    The Draft International Standard of The Inter- national Organization of Standardization, ISO/DIS 7933 "Analytical determination and interpretation of thermal stress using calculation of required sweat rates---Hot environments" has been distributed among countries. In this publication differences of thermal responses among races do not seem to be seriously taken into account. The authors wish to introduce data based on sweating abilities and want to discuss the importance of the thermal responses among races.


    Active sweat glands in different races

    Morimoto (1978) reported on earlier work on the racial variation in the total number of sweat glands by Kawahata (1943, 1951, 1961). This data is shown in Fig. 1. Sweating was activated by heat at 36-52C for 30-50 min and counts were taken at the maximum activation. The tendency for the total number of sweat glands to increase in people living in the tropics compared with those from northern latitudes is

    clearly shown, especially when one allows for differ- ences in skin surface area between the races. Schaffer et al. (1974) observed differences in the number of active glands between Eskimos and Caucasians using pharmacological activation of sweat glands. The difference of sweating response between Eskimos and Caucasians was approx. 1:2 on the trunk, 1:3 on the upper extremities, 1:4 on the lower extremities, and 1:5 over the feet.

    Ogawa (1987) reported on work done by Roberts et al. (1970) on the local distribution of sweat glands. Wide variation can be observed between different races (see Fig. 2).

    Sweat rate of subjects among different races and different living places of the same ethnic group

    Hori et al. (1975) studied physiological response to eat exposure of American, Japanese-American, and Japanese subjects living in the same climate. Caucasians and Japanese-Americans live in the same climate and approximately the same community in Santa Barbara, CA. Thus, if differences of physio- logical responses to heat between Caucasians and Japanese-Americans were found to exist, ethnic factors might be considered as a possible cause of



    1000 2000 3000 (x 103)




    Eskimo (Male)

    Negro (Male) (Residents in USA)

    Japanese (Residents in Japan)

    Eskimo (Female)

    Chinese in Formosa


    Caucasians (Male) (Residents in USA)


    1069 I

    1443 1991 I

    1636 1886 2137 I : I

    1727 1902 I t

    2179 20241 I

    1781 1- - - - - - -

    1771 I

    1783 I


    1800 I

    Caucasians (Female) (Residents in USA)

    Fig. 1. The total number of active sweat glands

    2077 I


    2282 2756

    2386 3068 I

    2415 I

    2422 I

    2469 2894

    2800 2642}"" -{~ 3062

    2478~ i123

    3415 I

    3121 I


    in different races (n/m2). From Morimoto (1978).

    the differences. Japan has hot, humid summers and cold winters. On the other hand, the climate of Santa Barbara is temperate in both summer and winter. It also follows that differences of physiological responses to heat between Japanese and Japanese- Americans might be due to differences, in the environmental conditions of their habitats. Young male subjects were exposed to a hot environment. Each subject dressed in shorts and resting in a supine position on a webbed cot, was exposed for a period of 2 h to 48C dry-bulb temperature with 22% relative humidity. Body weight loss was recorded continuously while the subject was on the cot, using a Brookline metabolic scale. To calculate the rate of evaporative sweat loss, the rate of weight loss was corrected for respiratory water loss and carbon dioxide production. The evaporative sweat loss for three groups with time were recorded. The mean value of evaporative sweat loss was largest for Caucasians and smallest for Japanese. The mean sweat loss per unit of body weight for Caucasians was 1.62%, that for Japanese was 1.25%, and that for Japanese-Americans was 1.48%. It is well-known that subjects sweat more in summer than in winter in Japan. Santa Barbara has a temperate climate

    with low humidity and ambient temperatures remaining within a narrow range all year round. Therefore, the temperate climate in Santa Barbara might have been responsible for the smaller sweat loss in Japanese when compared with that in Japanese-Americans.

    Morimoto (1978) reported that "racial differences in sweat rate have scarcely been studied because of the difficulty in obtaining the same experimental conditions in different laboratories". Observations under the same experimental conditions revealed that there was little (Gibson et al., 1948) or no (Herrman et ai., 1952) difference between the sweating ability of the white and Negro races. To assess the degree of heat stress under different experimental con- ditions, Asayama and Morimoto (unpublished data) utilized P4SR as an index of heat stress and compared sweating of Japanese with that of Caucasians (1967).


    There are considerable differences between the numbers of sweat glands among several races. However, it can not be clearly determined whether

  • Ethnic differences and response to thermal environment

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