Q: I’ve heard that washing your hair every day can strip it of its natural oils, making it dry and brittle and causing scalp irritation. Among them, he said, are your hair’s texture, how oily it gets, how processed it is, your lifestyle habits and your age. Shampoo cleanses your scalp and hair by removing environmental contaminants like dirt and pollen, as well as dandruff, sweat and hair-care products. It also dissolves sebum, an oily, waxy substance produced by the sebaceous glands near your hair follicles. Sebum keeps your scalp from becoming too dry, said Dr. Rosemarie Ingleton, an assistant clinical professor of dermatology at Mount Sinai Hospital in New York City, and protects the skin from infection.

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Persons: I’ve, Murad Alam, Rosemarie Ingleton Organizations: Northwestern University Feinberg School of Medicine, Mount Sinai Locations: Mount, New York City