Question

what is the function of human body hairs

Answer 1

Human hairs do function in thermoregulation. They 'trap' a thin layer of air close to the surface of the skin which sort of buffers the skin against dramatic differences in temperature in the surrounding environment but this function is thought to be something of an evolutionary 'left over.'

Their real role is in sensitivity. Each hair is attached to a very small neuron. If the hair is bent or touched, the nerve cell depolarizes and tells the brain that the body is being touched at this point. This might seem silly, but think how important it was to people in an evolutionary context where the organism touching the hair might be a malaria carrying mosquito.