Next to each hair is a sebaceous gland which secrete sebum which lubricates the hair and provides each hair with an element of protection. If the sebaceous glands are overactive greasy or oily hair will result. If the glands are underactive dry hair may result including breakage.
Daily Hair Tip
To keep bad hair days at bay, get regular trims and condition your hair, at least the ends, every time you shampoo.