Every single hair on your body grows from its own individual hair follicle. Inside the follicular unit, new hair cells are generated at the root of the hair shaft. As the new cells form, they force the older cells out of the follicle. As they’re pushed out, the cells die and become the hair that we see. The hair on your arms stays short because the cells that produce these hairs are biologically instructed to stop growing about every couple of months. As for the hair follicles on your head, they are programmed to continue growing for years at a time, so these hairs can grow to be very long. If you’re trying to grow out your hair, be patient! Each hair on your head grows for 2 to 6 years at a rate of only about ¼ to ½ inch each month. Your hair grows in repeated cycles. On average, 90% of the hairs are in a growth phase, and for the remaining 10%, they rest, shed and start growing again. Keep your hair healthy by regularly shampooing and conditioning, with the frequency and product selection dictated by your hair type. Also, minimize your hair’s exposure to heat and chemical treatments.