What is the primary factor that causes hair to grow?

The primary factor that causes hair to grow is the blood vessels feeding the hair root. This is because hair growth occurs in the hair follicle, where the hair root is located. Blood vessels supply essential nutrients and oxygen needed for the cells in the hair bulb to divide and produce new hair cells. This process is critical for maintaining healthy hair growth.

While a healthy diet can support overall hair health by providing the necessary vitamins and minerals, it is not the direct cause of hair growth. Similarly, proper hair care products can improve the appearance and condition of hair but do not influence the growth process itself. Regular haircuts can help manage split ends and maintain style, but they do not have a physiological effect on hair growth. Therefore, the nourishment and support from blood vessels are vital for promoting hair growth effectively.