How does shampoo clean my hair?

Lather, rinse and repeat ... really?

How do shampoos clean hair, and if repeated, would we ever finish washing our hair? Actually, it is not necessary to lather hair more than once -- only when excessive hair product or dirt is a problem.

"Shampoo molecules bond with seba.ceous dirt [on the hair] and both are then carried away when you rinse," said Rob Replogle of Silver Scissors Styling Salon, 159 S. Garner St. "Remember the monkeys from Wizard of Oz? They are sort of like that."

Ingredients to watch for include ammonium lauryl sulfate, which is a detergent which cleanses hair, guar hydroxypropyltrimonium chloride, which adds volume and smoothes hair, and dimethicone which coats to soften hair. Ammonium lauryl sulfate is a harsh product, while sodium laureth sulfate is a more mild detergent.

Most shampoos are about 80 to 90 percent water, 2 to 8 percent detergents and about 1 percent added fragrance. The amount of lather is not a clue to cleansing ability.

Lather forms when the shampoo detergent gathers around air instead of oil. Dirt and oil destroy lather. Having clouds of lather means too much shampoo has been used. Some people find their hair becoming dull over time, and that can be due to shampoo.

"The hair has cuticle layers similar to the bark of a tree," Replogle said. "People get dull build up because the [shampoo] molecules get trapped in that bark and can't get out. You need to use something that will open up the bark and release those molecules."

Hairstyle mandates how many times a week hair should be washed. Curly hair can become dry and frizzy if washed too often. Similarly, straight hair can become greasy and flat if washed too little.

Wonderin' how something works? Send questions for 'Inner Workings' to eca905@psu.edu.