Skin irritation, redness, scabs, a lot of itching, and scratching. To know if your dog has fleas, you need to examine your dog's skin and look if your dog has fleas or not. If you find any tiny, dark insects in your dog's skin, it means it is a flea. You will find them near the armpit or groin area mostly. Try combing your dog's fur with a fine-tooth comb or a brush. It will help remove the fleas from the skin and give some relief to your dog.