CLEANLINESS may be a virtue, but when it comes to hair? Apparently, not so much.

For Allison Drescher, a consultant in Boston, shampooing has become a weekly ritual she outsources.

“I get it washed and blown out once a week,” Ms. Drescher, 35, said. “It’s just one less thing to worry about day to day.”

Her stylist, Jeffrey Lyle at Emerge Spa and Salon, suggested it for convenience and for allure. “When it’s a little dirty, it actually looks smoother and shinier,” Mr. Lyle said.

Decades ago, a hairdresser’s most loyal customers  the Norms and Cliffs of salons  were grannies who would regularly come in to have their hair shampooed and set. For generations, the very idea of shampooing at home was almost taboo.