Yes, you can! A guinea pig's skin is very sensitive and more alkaline (basic) than a dog or cat so many dog shampoos will be very drying for guinea pigs.  Almost all human shampoos and many dog shampoos are too acidic for a dog or cat (or any small animal). When you use a product that is too acidic (the pH is 6 or lower), the protective layer of a dogs skin becomes irritated and causes them to scratch because they are itchy. Prolonged use of that type of product can actually destroy the protective layer and become a gateway for all kinds of skin infections and other conditions.  That's why it is so important to never use human products on dogs, cats, or guinea pigs!