There are two basic reasons for dry hair.
One is that your scalp doesn’t produce enough natural oil to moisturize and hydrate your hair. This can be hereditary, or it could be something that happens over time, because as we age, the body’s rate of oil production naturally slows down, leading to dryer skin and of course, dry hair.
It’s also possible that the condition or structure of your hair is causing the moisture to escape, which leads to dry and frizzy hair. A strand of hair is made up of three main segments. At the center is the medulla or core, which is the supporting structure. Surrounding the medulla is the cortex, which forms the middle layer. The cortex gives your hair its shape, versatility, flexibility, and twist.
Surrounding and protecting the cortex is the cuticle. Think of the cuticle structure as overlapping shingles on a roof. When the “shingles” are conservative, the hair seems lustrous and gleaming and dampness can’t escape. When the “shingles” are released, hair can seem dull and flyaway, and it’s simpler for characteristic oil and dampness to escape from the inward structure, which prompts debilitated and dry hair and hair fall.