We have about 100,000 hairs on our heads. Each hair shaft has three layers, with the cuticle, or outside layer, protecting the two inner layers.
Shiny hair is a sign of health because the layers of the cuticle lie flat and reflect light. When the scales of the cuticle lie flat they overlap tightly, so the inner layers are well protected from heat, sun, chlorine, and all the other hazards that can come from living in our environment.
When hair is damaged, though, the scales may separate and hair can become dry. Because the scales on dry hair don’t protect the inner two layers as well, hair can break and look dull.
The type of hair a person has — whether it’s straight or curly — can also affect how shiny it is. Sebum, which is the natural oil on the hair, covers straight hair better than curly hair, which is why straight hair can appear shinier.
Depending how long a person’s hair is or how fast it grows, the end of each hair shaft can be a couple of years old. So the hair at the end of the shaft could have survived a few summers of scorching sun and saltwater and winters of cold, dry air. How well you care for your hair from the time it emerges from the root plays a role in how healthy it looks.