Petex Moisturizing Dog Shampoo. Best Overall Shampoo. Buddy Wash's all-natural dog shampoo is the most effective and surprisingly affordable shampoo for common dry skin issues. The first rule of dog washing is not to use human shampoo. The pH of dog skin is very different from that of human skin. While our skin has a pH of around 5.5 to 5.6, your dog's skin is much more neutral, averaging a pH of between 6.2 and 7.4.