Answer:
In cold weather, heat can leave your body more quickly, which can lead to serious health problems like hypothermia and frostbite. To stay warm our body muscles begin to shiver causing fiction within the muscles to create warmth for our body.
As for animals when animals are in cold weather, it can affect them differently. Physiological changes occur, they build body fat, grow thicker fur, and create a sort of patch of air against the skin beneath the fur/ feathers. But if they fail to do so can lead to a fatal end or the animal.
I hope this helps :)