Shampoo and water act together to cleanse the hair by use of the shampoo molecule which has detergent molecules. A shampoo molecule has two ends: one hydrophilic and the other hydrophobic. The hydrophobic molecule attaches itself to the water while the hydrophilic molecule attracts the grease from the hair. The dirt is held by the grease and rinsed off by the water leaving the hair clean.
How shampoo and water act together to cleanse the hair? – http://wiki.answers.com/Q/How_shampoo_and_water_act_together_to_cleanse_the_hair