Hair contains a protein called keratin. This same keratin also composes the skin and nails. Hair is also like skin in that it contains three main layers.
The layer in the center of the hair shaft is the medulla. The medulla is made up of round, circular cells that can sometimes appear empty.
The middle, second layer of a strand of hair is called the cortex. The cortex contains a lot of cells that are joined together. This cortex helps to support the hair's strength and also makes up the biggest portion of the hair.
The outside layer of hair is the cuticle. Much like a nail cuticle, the hair cuticle acts as a protectant, in that it protects the other two inner layers of the hair. The hair cuticle is not visible.
Every hair grows from a hair follicle, a pocket-like area of the skin that has what looks like a bulb. The center of that bulb is a papilla. It is the job of the blood vessels of the papilla to give nutrients and oxygen to the hair.
Hair and Oil
The glands around the hair shaft, the sebaceous glands, secrete oil. This oil is called sebum. This sebum provides a benefit to the hair. This benefit includes keeping hair shiny, protected and water-resistant.
Sometimes people put oil in their hair in an effort to moisturize and protect the hair. There is also the common misconception that hair absorbs oil. While hair does not technically absorb the oil, the oil does coat the hair. The oil is unable to completely absorb into the hair. Instead, the oil coats the hair by latching onto cracks and holes in the hair shaft. The hair has a scaly surface which allows the oil to penetrate the hair as it slides down the hair and slips into those cracks. Think of it like wearing a coat. A coat will protect you, but you would not actually absorb the coat. Hair and oil work in a similar manner. The hair is protected by the oil but is not absorbed.
Moisturizing Hair With Oil
Moisturize and protect the hair with oil. Either buy a hot oil treatment at the local drugstore or make your own with olive oil. Simply apply the oil to the hair, let sit for 10 to 15 minutes, and then wash twice in the shower to remove remaining traces of oil. There should be no need for conditioner.