It can depend on the context. For instance, what does "it" refer to? If you have a spot of oil on your scalp, apply some amount of shampoo on the scalp and then wash it off. --> "It" refers to the "spot of oil". In this case, using "wash" is correct, because you are washing off the spot of oil. Apply some amount of shampoo on the scalp and then wash it off. --> "It" could refer to "shampoo" or something else from an earlier sentence. If "it" refers to "shampoo", then you can use "rinse" or "wash". You are correct. "Rinse" means to clean off with water. But we often say "wash" to mean the same thing. After you get out of the ocean, rinse off the salt (with water). <-- Natural After you get out of the ocean, wash off the salt (with water). <-- Natural

Wash = clean something usually using soap - this involves the whole process of water, water + soap, followed by the rinsing out of the soap Rinse = remove something using water - this refers to removing either dirt/dust etc or the soap/shampoo used for washing Wash off/ wash out = the same as rinse The instructions are perfectly correct - 'wash off' here means the same as rinse. Rinse is actually more thorough than wash off, and involves quite a lot of water. For instruction for something such as skin cream, 'wash off' is more accurate.

Technically you are right but we would actually say both. In this case, putting the shampoo on, rubbing it in, and rinsing with water are all part of the process of washing your hair so the action of massaging the shampoo into your hair whilst rinsing it off can also be seen as washing it off.