What is the primary function of hair on the scalp?

The primary function of hair on the scalp is to protect the scalp from sunlight. Hair acts as a barrier against harmful ultraviolet (UV) rays, which can lead to skin damage and increase the risk of skin cancer. The dense covering of hair helps to shade the skin of the scalp, reducing direct exposure to sunlight.

While insulation and heat regulation are also important functions associated with hair, in the specific context of scalp hair, protection from UV radiation is a more direct and critical role. Additionally, scalp hair does not absorb moisture significantly; rather, it can sometimes hold moisture temporarily but doesn't play a key role in managing hydration for the scalp. Thus, the protective function against sunlight stands out as the foremost role of hair on the scalp.