Some people believe it is necessary to switch shampoo brands every now and then to keep the hair looking shiny and bouncy. Although there is no valid reason to think hair becomes “immune” or “resistant” when we use the same shampoo day in and day out, there may be other reasons people might want to vary their hair-washing routine, according to one expert, Nicole Rogers, an assistant clinical professor of dermatology at Tulane University School of Medicine in New Orleans.

A Deep Cleanse

To remove environmental pollutants and natural oils from the hair, shampoos typically contain a powerful cleansing agent, usually a sulfate-based chemical, which attracts both oil and water, Dr. Rogers says. Of the two main types, lauryl sulfates are designed for oily hair while laureth sulfates are for normal to dry hair—still a good cleanser but slightly less drying, she says. Sudsing up in the shower draws dirt and oil from the hair and sends it down the drain. “Sulfate-based cleansers lather well and rinse well and historically they’ve been popular,” she says.

There has been growing concern that those chemicals can harm the skin or scalp. (Rumors they are carcinogenic have been widely debunked, Dr. Rogers says.) “The only danger ever proven is that sulfates can be a topical allergen to people who are already prone to having sensitive skin,” says Dr. Rogers, who also maintains a dermatology practice in Metairie, La.

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