When running, the body will continuously generate heat, at the same time, the metabolism of various parts of the body will increase, and the oxygen consumption will also increase. This will make the pores of the body expand (sweating, heat dissipation), and the breathing will gradually increase and deepen to shortness (oxygen absorption).
Talking about rain and cloudy days: First of all, rain is formed by water droplets formed by tiny suspended particles (basically harmful substances such as dust and impurities) attached to the air. On cloudy days (including when it rains lightly), the air pressure is relatively low, so the oxygen content in the air is relatively low and other harmful substances are relatively dense.
So imagine what would happen if you ran in the rain.
Impurities, bacteria, harmful substances and harmful parts in the air can invade your body from your skin and breath. The result can be imagined!
Some people will say, this is nothing! I did it! I'm not sick! Yes, some people are in good health! He didn't feel anything after doing this once. But don't forget, nothing this time doesn't mean he won't do anything in the future. Everything has an accumulation process, from quantitative change to qualitative change.
That's all, typing is too tired! end