Fleas are more than an irritation; they can cause a range of illnesses in dogs. The problem is that, unless they are allergic to flea saliva, dogs don’t always scratch when they have fleas. To complicate matters more, fleas are sly and great at hiding. So how can you determine if your dog has fleas?

Know Where the Fleas Like to Gather
The most common congregating spot for fleas is around the base of your dog’s tail and her lower back. You can certainly find them anywhere on your dog’s body but if there are only a few fleas and you want the best chance of finding them, start there.
Push the Fur Backwards to Get a Better View
Fleas don’t waste much time on top of your dog’s fur. They need to get down to your dog’s skin in order to sink their mouthparts into their host and drink blood. The best way for you to see your dog’s skin is to gently push the fur backwards with your hand.

Don’t Center All of Your Hopes on Seeing an Actual Flea
Fleas are sneaky and there aren’t always very many of them on your dog at once. You’ll need to put on your detective hat and look for more than just live fleas. The other evidence that these pesky pests are nibbling on your canine pal is their excrement. They leave flea feces wherever they go.
Flea stool impersonates small specks of black dirt, so it is called “flea dirt.”
Look for and collect any dirt that you find during your visual flea hunt and also when you search with a flea comb
If you take some of the dirt look-a-likes, place them on a white paper towel, sprinkle water on them, then give them a little rub, you will see red smudges appear. This is a definitive answer for you: your dog has fleas. The reason the flea dirt turns red is because it is just digested blood.
If you haven’t spotted fleas or flea dirt at this point, grab a flea comb and run it all over your dog, stopping every swipe or two to examine the comb’s tines. Look for fleas and flea dirt. Fleas can slip through the bristles of a regular brush, but a flea comb’s tines are too close together for the critters to squeeze between. You can catch them this way, but be ready to put them in some soapy water or squish them really hard.