My dog's super senior (like, really, really old - she's 19!!!) and flea prevention gives her seizures, so we switched her from preventatives to weekly washing and eliminated all "bad" chemicals from her environment. We were using a natural shampoo before but it would only zap fleas for the time of washing, and they would reanimate later on, but with this one they were actually falling off when she was drying on a blanket. Not killing all the fleas entirely, I still could find one or two the next day, but much better than before on a different natural shampoo. The foam is rich, forms instantly, so you don't have to rub it for ever, and the smell is nice.