Now, first of all, Herbal Essences is a very early 70s brand from a time when herbal tea was considered about as exotic as Devandra Benhart. Of course, herbal essence later became a nickname for another herbal substance often smoked in bongs. But then, let's stick with this shampoo. 
So you got a brand that's "that 70s brand" and you need something hip, fun, maybe a little quirky. How about some wordplay, alliteration and a little science stuff too for kicks! Does it make ANY sense at all. I think not. What exactly do these 2 words mean? Think about it: "H E L L O H Y D R A T I O N ? ? ! !"