A: Shampoos are designed with cleansing agents called surfactants. A surfactant
molecule has a hydrophilic (water attracting) "head" and a lipophylic (oil attracting) "tail".
When you apply the shampoo and water to the hair and generate lather, the hydrophilic
head of the surfactant is drawn to the water, while the lipophylic tail is drawn to the oil and grease on the hair and scalp.
This oil and grease contains dirt and skin particles. The lathering action of the
"head" and "tail" of the surfactant creates a push and pull effect on the oil and grease,
lifting it from the hair shaft. The more oil and grease there is to bond to the surfactant
molecule the less the shampoo will lather. This is why a second shampooing alwayslathers more richly.
When you rinse away the shampoo, the water is pulled along by the hydrophilic
head of the surfactant, away from the hair and scalp, and down the drain.