Most Likely: According to New York City veterinarian Jennifer Gabriele, eight times out of 10 nothing will happen if you and Muffin share hair products. In fact, some groomers and breeders prefer human shampoo to dog shampoo, using products like Head & Shoulders (to prevent dandruff) and Pantene (for a silkier coat). Just make sure your dog doesn't have sensitive skin.

Worst Case: If your dog is allergic to ingredients in the human shampoo, he could develop a rash, swollen skin, or, in very rare instances, severe breathing problems.