What is the use of shampoo; is it for the hair or for the scalp?
We shampoo our hair because of sebum. In humans, sebaceous glands are most numerous on the face and scalp, with (on the scalp at least) several glands plus a hair follicle making up a pilosebaceous unit.
Each gland secretes sebum, initially a colorless and odorless fatty substance (plus dead cells) that spreads from the scalp outward over the hair, but that breaks down by bacteria producing strong odors.
Look at a person who has not washed their hair in a week and it will be easy to understand why we wash the &quot;dead&quot; stuff on our heads. It looks oily and it eventually smells bad as well.