Your statement is one-sided. Not all thin people have long hair. The length of hair has nothing to do with people's fatness. The length of body hair is related to heredity. Individuals vary greatly, as long as other physical characteristics are obvious, there is no problem.

The amount of body hair is also related to hormones. Female estrogen is strong, estrogen can inhibit the growth of body hair, while androgen can promote the growth of body hair.

The human body should regulate the internal temperature by sweating to keep it relatively stable with the external temperature, otherwise it will get sick.