The Thermal Response of the Skin to Radiation

Abstract

The thermal sensitivity of skin to radiation has been studied with a new technique and the temperature changes in the skin surface have been accurately measured. The change in skin response of both whites and negroes to visible, infrared radiation, and sunlight has been measured. Results show that the sensation evoked by the radiations depends upon the optical properties of the skin. White subjects were found to be more sensitive to heat than negroes. The effect of the exposed area upon the sensitivity was observed. The postulate that the magnitude of the sensation depends upon two factors, nerve impulse frequency and central association, was found to fit the present data. A formula for calculating the degree of association is proposed. The results show that the sensitivity to radiation increases as the exposed area is increased up to the point where the stimulus has dropped to 0.0004 gram cal./sec.·cm². A radiation weaker than this will evoke no sensation regardless of the size of the area exposed. This was taken to be the threshold of the excitation of an end organ. The temperature change in the skin surface with this radiation rate was measured to be a rise in temperature at the rate of 0.0008°C per second; sensation is perceived after 3 seconds of exposure. The relationship of the temperature change of the skin was studied. It was found that neither the change (ΔT) nor rate of change (ΔT/Δt) of skin temperature is adequate to explain the sensory effect. An hypothesis is proposed which attributes the sensation to a differential change in the temperature of the blood vessel net work within 0.1 mm of the skin surface and another at 0.3 mm.