The main function of human hair is protection from elements, predators and microbes in their environment that threaten safety and health. This is why humans develop hair in the most vital areas, such as the scalp, around the eyes, in the nose and ears, and around the genitals.

Eyebrows And Eyelashes

Eyebrows grow across the brow to protect eyes from water (rain) and perspiration that falls from the scalp and forehead. Eyelashes catch coarse particles that may enter the eyes.

Nose And Ear

Hair in the nose and ears also keeps dust particles out of the canals, preventing microbial infection.

Pubic And Underarm Hair

Hair in these regions lessons friction between body parts and limbs during movement. Hair in the underarm region also provides more surface area for evaporation of sweat, according to Dr. Kaur.

Volume/defense

Hair stands on its ends when one is in danger, thereby adding volume to the body, making it look bigger and more threatening to the predatory enemy. Scalp hair defends the head from sun damage or radiation, and rainfall by preventing water from getting into the skin.

Temperature

Hair helps regulate heat loss by acting as an insulator. When people are cold, brain impulses cause hairs to stand on end, thereby enclosing an insulating coat or layer of air just outside the skin. This layer reduces heat loss, according to Dr. Birendra Kaur.

Facial hair

In men, facial hair functions as a differentiating feature from the opposite sex. It serves as a decorating (peacock) feature.

Source:

sikhpoint: Human Hair - A Biological Necessity; Dr. Birendra Kaur