Hair is coated with a layer of sebum a natural oil produced by sebaceous gland lying next to each hair follicle in the scalp.

The sebum gives the hair its shine and also protects it from losing its own moisture content. The amount of oil secreted by the sebaceous glands determine whether the hair is dry, greasy or normal.

At the same time use of harsh shampoo, or dry windy weather can strip the natural oils from the scalp and hair leaving it dull and dry.

Source: Fashionpk.net