The word shampoo originates in India from the Hindi champo which means massage. It was first used by Hans Sloane (of Sloane Square fame who introduced several words into English including samurai and vivisection, as well as being a great fan of cocoa). In 1698 he describes what he calls champing as a massage instrument used in China. This idea of shampoo = massage was in vogue continuously for 150 years, often with an exotic flavour as something done in Asia.
In its current sense relating to cleaning hair, the word was first used in Worcester’s A Dictionary of the English Language which was published in Boston in 1860. For 30 years, this was the benchmark for dictionaries in America. It was the first American dictionary to include many diagrams and to provide synonyms. But at the beginning, having a shampoo was not much fun. Only soap was used. Later herbs were added.
Source EVS Translations:
http://www.evs-translations.com/blog-com/shampoo/