🧬 biology

Adaptive Differences in Cutaneous Thermal Sensations across Natural Climates: Cold, Temperate, and Tropical indigenes

This study demonstrates that long-term exposure to natural climates (tropical, temperate, and cold) induces adaptive differences in cutaneous thermal sensations among indigenous populations, with tropical indigenes exhibiting significantly higher thermal thresholds and lower sensitivity compared to those from colder regions, even when living in modernized environments.

Original authors: Sang-Hyun Roh, Syifa Salsabila, Titis Wijayanto, Joo-Young Lee

Published 2026-06-26

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Sang-Hyun Roh, Syifa Salsabila, Titis Wijayanto, Joo-Young Lee

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your skin is like a high-tech security system for your body. Its job is to constantly scan the environment and send alarms to your brain saying, "Hey, it's getting warm!" or "Ouch, that's too hot!"

This study asked a fascinating question: Does living in a specific climate for your whole life change how sensitive your security system is?

The researchers compared three groups of people, each representing a different "climate zone":

The Tropical Team: People from Indonesia (hot and humid year-round).
The Temperate Team: People from Korea (four distinct seasons).
The Cold Team: People from Mongolia (very cold winters).

They tested these groups by gently heating up their skin in two different ways: Contact Heat (touching a warm probe) and Radiant Heat (shining a heat lamp on them). They measured three specific "alarm levels":

Warmth: "I feel something nice and warm."
Hot: "This is getting intense."
Heat Pain: "Ouch! Stop, that hurts!"

Here is what they found, explained simply:

1. The "Desensitized" Tropical Team

The people from Indonesia acted like they had thick, heavy armor on their skin.

The Result: They needed the heat to get much hotter before they felt "Warm," "Hot," or "Painful."
The Analogy: Imagine trying to wake up a deep sleeper. You have to shake them a lot harder than someone who is lightly dozing. The Indonesian participants were the "deep sleepers" when it came to heat. Even though their skin was actually starting at a similar temperature to the others, they didn't sound the alarm until the temperature was significantly higher.
The "Hot" Spot: The biggest difference was in the "Hot" sensation. The tropical group was much less sensitive to feeling "hot" compared to the others.

2. The "Hyper-Aware" Cold Team

The people from Mongolia acted like they had super-sensitive, thin skin.

The Result: They felt the heat alarms go off much sooner. Even though their skin was actually slightly warmer at rest (perhaps because they are used to being cold), they still reacted to the heat faster than the others.
The Analogy: Think of them like a smoke detector that is set to "High Sensitivity." It goes off at the slightest hint of smoke. They felt "Warm," "Hot," and "Painful" at much lower temperatures than the Indonesian group.

3. The "Middle Ground" Team

The people from Korea fell right in the middle.

The Result: They were more sensitive than the Indonesians but less sensitive than the Mongolians. They were the "Goldilocks" of thermal sensation—not too thick-skinned, not too thin-skinned.

4. Where on the Body?

The researchers tested 17 different spots, from the forehead to the soles of the feet.

The Pattern: The differences were everywhere, except for the upper arm. The upper arm seemed to be the one place where everyone felt heat the same way, regardless of where they lived.
The Extremes: The differences were most obvious on the trunk (chest, back, belly) and the legs/feet.
The "Ghost" Effect: In the radiant heat test (the heat lamp), many Indonesian participants didn't even feel "Hot" or "Painful" even when the machine reached its maximum safety limit! It's as if their alarm system was so desensitized that it didn't even register the signal, whereas the Mongolians felt the pain clearly.

The Big Takeaway

The study concludes that your environment writes a new manual for your skin.

Even though these people were living in modern cities with air conditioning and heating, their bodies had retained the "memory" of their natural climate.

If you grew up in the heat, your body learned to ignore the heat to save energy, making you less sensitive to it.
If you grew up in the cold, your body stayed on high alert for temperature changes, making you more sensitive.

In short: Your skin isn't just a passive covering; it's a learned skill. Living in a tropical climate essentially "turns down the volume" on your heat sensors, while living in a cold climate keeps the volume "turned up."

Technical Summary: Adaptive Differences in Cutaneous Thermal Sensations across Natural Climates

Problem Statement
While the physiological effects of heat acclimation (short-term exposure) and heat acclimatization (long-term, lifetime exposure to natural climates) on thermoregulatory responses (e.g., sweating rates, core temperature) are well-documented, the impact of these adaptations on cutaneous thermal sensations remains under-investigated. Previous studies have explored ethnic differences in pain perception, but often within the same geographical region, making it difficult to isolate the effects of long-term climate exposure. Furthermore, no prior study has simultaneously compared cutaneous thermal thresholds across populations native to tropical, temperate, and cold climates, nor has it provided a comprehensive whole-body mapping of these sensations. This study addresses the gap in understanding how long-term exposure to distinct natural climates modifies the perception of warmth, hot, and heat pain sensations in indigenes living in modernized environments.

Methodology
The study employed a comparative experimental design involving three distinct indigenous groups:

Tropical: 14 Indonesian males (Yogyakarta, Indonesia).
Temperate: 15 Korean males (Seoul, South Korea).
Cold: 12 Mongolian males (Ulaanbaatar, Mongolia) for contact heat; 14 Mongolian males for radiant heat.

Experiments were conducted during the warmest months in each location to minimize seasonal variation. Participants underwent two distinct testing protocols:

Contact Heat Test: Conducted on all three groups (41 subjects total). A thermal stimulator (6.25 cm²) was applied to 17 body regions. The probe temperature increased at a constant rate of 0.1°C/s. Subjects pressed a button to record thresholds for initial warmth, hot, and heat pain sensations.
Radiant Heat Test: Conducted on Indonesian and Mongolian groups (28 subjects total). A radiant heat panel (100 cm²) was positioned 10 cm from the skin, increasing surface temperature at 1°C/s. Local skin temperature ( $T_{sk}$ ) was recorded at the moment of sensation onset.

Key Contributions

First Simultaneous Comparison: This is the first study to simultaneously compare cutaneous thermal thresholds among populations from tropical, temperate, and cold climates.
Whole-Body Mapping: The study provides the first comprehensive mapping of cutaneous thermal thresholds across 17 distinct body regions, moving beyond localized or whole-body average measurements.
Differentiation of Sensation Levels: The research distinguishes between thermal sensitivity at different sensation levels (warmth, hot, and heat pain), revealing that adaptation effects are not uniform across all sensation types.

Results

Thermal Thresholds and Sensitivity:
- Indonesians (Tropical) exhibited significantly higher thermal thresholds (requiring higher $T_{sk}$ to perceive sensation) and greater thermal insensitivity (larger $\Delta T_{sk}$ from baseline to threshold) compared to Mongolians (Cold) in both contact and radiant heat tests ( $P<0.05$ ).
- Koreans (Temperate) demonstrated an intermediate level of thermal sensitivity: they were more sensitive than Indonesians but less sensitive than Mongolians.
Regional Variations:
- Contact Heat: Group differences were prevalent across all 17 body regions for warmth, hot, and heat pain, with the exception of the upper arm, where no significant differences were found.
- Radiant Heat: Differences were most pronounced in the trunk and distal legs. Indonesians showed significantly higher thresholds and lower sensitivity over a broader range of body regions compared to Mongolians.
Sensation Specificity: The most extensive group differences were observed for hot sensations rather than warmth or heat pain. This suggests that physiological desensitization from heat acclimatization is most clearly manifested in the perception of intense heat, occurring after the non-noxious warmth level but before the noxious pain level.
Non-Responders: In the radiant heat test, a substantial number of Indonesian subjects did not perceive hot or heat pain sensations even when the panel reached its safety limit (230°C), whereas Mongolian subjects consistently perceived these sensations within the limit. This implies the actual thresholds for tropical indigenes may be even higher than measured.
Baseline Skin Temperature: Despite Mongolians having slightly higher resting skin temperatures in distal regions compared to other groups, they consistently showed the lowest thermal thresholds, indicating higher sensitivity.

Significance and Claims
The authors claim that these findings demonstrate that long-term exposure to natural climates induces a desensitization of cutaneous thermal sensations, a characteristic that persists even when populations reside in modernized environments. The study posits that these differences are primarily derived from heat acclimatization rather than innate biological variations in nerve fiber density, citing literature that shows similar epidermal innervation across ethnicities.

The paper concludes that understanding these climate-dependent differences is crucial for:

Improving the understanding of behavioral thermoregulation among populations in different climatic regions.
Providing a scientific basis for establishing appropriate indoor cooling and heating temperature standards, particularly during extreme weather events like heat waves and cold spells.

The authors remain modest regarding the scope, noting that the study did not investigate cold stimuli and that the "non-responder" data for Indonesians suggests their true thresholds may be even higher than recorded. They emphasize that while the study establishes a baseline for heat perception, further research is needed to fully understand cold adaptation mechanisms.