Why do some people tolerate the heat poorly, while others are delighted when the weather is very hot?

The contrast can indeed be enormous: while one person is panting in the shade at 30 °C, another only truly comes alive. This difference isn’t a matter of complaining or "character"—it is driven by a complex interplay of biology, physiology, and lifestyle.

Our body regulates its temperature via the hypothalamus, a sort of internal thermostat in our brain. Why this thermostat reacts differently for everyone comes down to the following factors:

1. The Cooling System: Sweat Production and Blood Vessels

To get rid of excess heat, the body relies on two main mechanisms: dilating blood vessels in the skin (which releases heat into the air) and sweating (the evaporation of moisture cools the skin).

• Fit and active people generally sweat faster and more efficiently. Because of exercise or training, their bodies are used to a higher core temperature and kick-start the cooling process much earlier.

• Hormonal fluctuations (such as during menopause or due to an overactive thyroid) can disrupt the internal thermostat. An overactive thyroid accelerates metabolism, making a person feel much warmer from the inside out, meaning they tolerate external heat poorly.

2. Body Composition and Body Fat

Body fat acts as an insulating layer.

• People with a higher body fat percentage retain their internal body heat more easily. While this is an advantage in the winter, in the summer it acts like a heavy winter coat that you cannot take off.

• Additionally, the ratio between skin surface area and body volume plays a role. Smaller or leaner people relatively have more skin surface per kilogram of body weight, allowing them to release heat into the environment more easily.

3. Acclimatization (Habituation)

The body needs time to adapt to the heat. This biological process takes about 10 to 14 days.

• For someone who spends a lot of time outdoors or has just returned from a tropical vacation, the body has already adjusted: blood volume increases slightly (so the heart doesn't have to pump as hard to send blood to the skin) and sweat glands excrete fewer salts, preventing rapid dehydration.

• Anyone who constantly stays in air conditioning doesn't give their body the chance to acclimatize and will react much more severely to a sudden heatwave.

4. Age and Medication

As we age, the elasticity of our blood vessels decreases, and the sensitivity of both our sweat glands and our thirst reflex declines. Consequently, older adults face a greater physical challenge in keeping their core temperature stable. Certain medications, such as diuretics or blood pressure drugs, also affect fluid balance and make the body more sensitive to heat.

Did you know? When your body is properly acclimatized to the heat, your internal core temperature in the morning is actually about 0.3 °C lower on average. You literally start the day with a built-in "pre-cooling" system.

(source: Google Gemini)