Most dry shampoos work by absorbing the excess oils and grease which accumulate on a dog’s coat. Powder dry shampoos use starches or clay to soak up these chemicals. Foams, gels, and sprays, on the other hand, make use of gentle surfactants – the same type of chemical used in face washes and other cleansers – to break down these oils so they can be rubbed or brushed away. The gels, foams, and sprays also’ rinse’ residues such as mud and leaves. Some dry shampoos also contain plant extracts that kill odor-causing bacteria, leaving your dog smelling fresh.