Dry hair can be caused by scalp oil that has trouble covering the surface of your hair.
Is there a natural cause for dry hair? Hair dryness depends on your scalp condition, your age, gender, and the health of your scalp. Scalp “oils” are a combination of various-sized fatty acids and other fat-based molecules.
With dry hair, there can be a difference in the chemical composition of scalp “oils” which does not allow them to distribute as well over the hair surface. There may be little to no difference in how much oil (sebum) is produced on a head with very curly hair versus a head with very straight hair. Oiliness may be more obvious on straight hair, however, since oil is more easily distributed over a smooth surface.