Perhaps you've had this experience: at the same temperature in spring and autumn, the sensations are profoundly different. In spring, when the morning temperature is only 10 degrees Celsius, we walk easily in the sunlight under thin clothing, and soon beads of sweat appear on our foreheads; however, come autumn, in the cool of a 50-degree Fahrenheit morning, even wrapped in coats, a breeze can make us begin to shiver.

This phenomenon is often attributed by people to the change of seasons based on experience. After a summer, people have become accustomed to the heat, and at the beginning of autumn, a temperature of 50 degrees Fahrenheit feels chilly compared to the scorching summer. Conversely, after the cold baptism of winter, spring feels warm despite not having high temperatures, relative to the icy winter days. Although this explanation is somewhat subjective, scientific research also indicates that the human body indeed goes through an adaptation process in its perception of temperature.

To delve deeper into the reasons behind this "same temperature, different feelings," it is necessary to first understand the physiological response of the body to cold temperatures. The decrease in temperature is first perceived by temperature receptors on the skin and conveyed to the hypothalamus in the brain. Although the hypothalamus accounts for only about 0.3% of the brain's mass, it plays a significant role in regulating body temperature, eating, reproduction, and endocrine activity.

Facing the cold, the hypothalamus sends out signals that prompt the body to initiate two main responses: one is vasoconstriction, especially of the blood vessels in the skin and other peripheral areas, to reduce heat loss; the other is shivering muscles, where rapid muscle contractions generate heat, which is why people shiver in cold weather.

Given this, scientists, by observing the reactions of vasoconstriction and shivering, have studied whether the human body increases its tolerance to cold after prolonged exposure to cold environments. It has been found that people living in cold regions, such as the Arctic natives, show less vasoconstriction and shivering when encountering low temperatures, suggesting that they have adapted to the cold environment. Additionally, fishermen who work in cold water for extended periods also demonstrate adaptation to the cold; when they immerse their hands in ice water, their hand temperature is slightly higher than that of the average person.

Therefore, after a long winter, our bodies seem to have adapted to the cold by the time we greet spring, feeling hot at even a slightly elevated temperature; conversely, after a hot summer, we are unprepared for the cold, and the arrival of autumn winds feels bone-chillingly cold. This adaptation is usually accomplished through the regulation of the nervous system. However, sometimes the body also undergoes physiological changes with repeated exposure to cold, such as an increase in cold tolerance related to "brown fat."

The fat in the human body can be divided roughly into two types: white fat and brown fat. The so-called "body fat" is actually white fat, which primarily serves as energy storage, whereas brown fat plays a role in generating body heat.