A diet lacking in vitamins and protein can cause hair to become dry and make it more prone to breakages.
This is because your hair needs a variety of nutrients to grow and repair itself, including vitamins A, C, D, and E.
Hormonal changes in the body caused by things such as pregnancy, the menopause and birth control can have undesirable effects on the hair.
If your dry hair is caused by hormones, you may also feel fatigued, colder than usual, weaker and your hair may begin to fall out.
This is something best talked about with a doctor if you feel like this might be causing your dry hair.