Cutaneous thermal thresholds of tropical indigenes residing in Japan

The purpose of this study was to examine the deacclimatization of the cutaneous thermal sensations of tropical indigenes residing in temperate climates. Tropical indigenes (n=13) who were born and raised in tropics but had resided in Japan for 5–61 months participated in this study, along with temperate indigenes (n=11). Their cutaneous thermal thresholds for warm, cool, hot, and cold sensations were measured in 12 body regions using a thermal stimulator controlled by a Peltier element and a push button switch. Subjects pressed the button-switch as soon as they perceived a feeling of being ‘slightly warm’, ‘slightly cool’, ‘hot’, or ‘cold’ from a neutral thermal state. Our results showed that: (1) among the tropical indigenes, no significant relationship was found between the duration of their stay in Japan and their cutaneous thermal thresholds; (2) the tropical indigenes were, on average, 3.3, 3.5, 4.2, and 7.3 °C less sensitive to warm, hot, cool, and cold sensations, respectively, than the temperate indigenes (P<0.05); and (3) the inter-threshold sensory zones between cutaneous warmth and coolness, and hot and cold sensations were wider among the tropical indigenes than among the temperate indigenes. It was concluded that the nature of the heat acclimatization of the cutaneous thermal thresholds for the tropical indigenes was retained despite their residence in a temperate climate for up to 61 months, indicating that they had more blunted perceptions of both warming and cooling than the temperate indigenes.

► No significance exists between the residence duration in Japan and thermal sensation.
► Tropical natives are less sensitive to warm/cool sensations than temperate natives.
► Inter-threshold sensory zone is wider in tropical natives than in temperate natives.
► Heat acclimatization of the tropical is retained for up to 5 year residence in Japan.