Flea allergy dermatitis (FAD) is a condition in which your dog is hypersensitive to the saliva of fleas.

FAD can be triggered by only one bite from a flea, and it will cause your dog to be extremely itchy and likely to have inflamed skin covered in tiny red bumps. Generally, the inflamed skin will be on back of your dog’s thighs, the sides and bottom of his abdomen, and along his back.

Without proper flea protection, all dogs are at-risk for getting fleas. However, it is not clear why some dogs are hypersensitive to flea saliva.