Why do people sweat easily when the weather is hot?

The human body perspires for the need of heat dissipation. In hot weather, in order to protect themselves, the human body mainly radiates heat in two ways.

1, direct heat dissipation:

When the surface temperature of the human body is higher than the ambient temperature, the heat generated by the human body can be radiated to the external environment in the following three ways: one is to directly radiate the heat to the outside in the form of heat rays, which is called radiation heat dissipation; The second is that the heat is directly transferred to the cold objects in contact with the human body, which is called conduction heat dissipation. The second is that the heat is taken away by the cold air around the body surface, which is called convective heat dissipation. Under the climatic conditions in most parts of China, except in hot summer, the temperature of the external environment is generally lower than the body surface temperature, so the heat lost through the above three ways accounts for about 85% of the total heat dissipation of the human body. How much heat the human body directly loses through the skin depends on the temperature difference between the skin surface and the external environment, and the temperature of the human body surface can be controlled by changing the amount of blood flowing through the skin. When the blood vessels in the skin are relaxed and the blood flow is large, the body surface temperature is high; Skin blood vessels contract and the blood flow is small, so the body surface temperature is low. Therefore, the human body can change the heat dissipation of the human body in a considerable range by changing the contraction state of skin blood vessels.

(2) Evaporation and heat dissipation

Evaporation is the process by which a substance changes from a liquid to a gas. Evaporation requires heat, at room temperature, 1.

Water evaporates from the skin surface and is absorbed by the body.

KJ is hot, so evaporation is a very effective way to dissipate heat. The total amount of evaporation depends on body surface area, skin temperature, air temperature and air flow. Air flow not only accelerates convective heat dissipation, but more importantly, it takes away the water vapor near the skin and promotes the evaporation of water, resulting in greater heat dissipation. This is the reason for sweating. Sweat evaporates at any time, showing recessive sweating; The evaporation rate is slow, and the water droplets gather into water droplets, which obviously perspires.

Humidity has the opposite effect. The higher the humidity, the lower the evaporation. When the air temperature and the temperature of the surrounding objects are close to body temperature, both radiation and convection lose their functions, and then the heat dissipation depends entirely on evaporation.

Wish you all the best!