What to Know About Fleas

Medically Reviewed by Amy Flowers, DVM on February 12, 2024
11 min read

The problem begins with some scratching here and there. Maybe you spot some tiny specks around the house that you might’ve missed before. Maybe your pet's beautiful hair that was so thick is looking a tad thin these days. Before you know it … yep. It’s confirmed.

Fido has fleas. And you’d better check Fluffy the Cat, too.

More than 2,000 species of fleas exist throughout the world, yet one is the most common among American dogs and cats. It’s called Ctenocephalides felis, or the cat flea.

That’s right. If your dog has fleas, they’re most likely cat fleas. So, what do they look like?

Fleas are tiny wingless parasites that survive by sucking on animal or human blood. They find new hosts to live on by searching for body heat, movements, and breathing. (Fleas usually can't see well.) Once fleas detect a new host, they jump onto its skin, fur, or feathers. 

A couple of fleas on your dog can morph into many more. After sucking some of your dog's blood, adult fleas will mate and lay eggs in its fur. These eggs often fall off your dog as it moves around. Once these eggs hatch into larvae, they find a place (say, a crack in a dog bed) to crawl into and make a cocoon. In a few weeks, they become adult fleas looking for hosts to jump onto, to eat blood, and to lay more eggs. Fleas also spread diseases.

Where do fleas come from?

Outdoors, fleas like warm, humid places to wait for hosts. They'll live in trees, shrubs, and tall grass. Urban wildlife like raccoons, foxes, and squirrels may have fleas, and your dog may be drawn to places where these animals live. 

Indoors, fleas like places where your pet might sleep or rest, like kennels or a favorite bush or porch spot.

Fleas can remain inactive for a long time, waiting for the weather to warm up or the right host to pass by.

Fleas are about 1/8 to 1/12 inch long, wingless, and brown or black in color. They have hard bodies, large hind legs, and look flat. This body type allows them to move easily between the fur or feathers on their animal host. Fleas also have piercing mouth parts for sucking blood and flexible spines that lock into animal fur, making it difficult to pull them off.

Do fleas fly?

Fleas don't fly. Instead, they are amazing jumpers. They can jump up to 7 inches high and up to 13 inches across a flat surface. That's about 200 times their body length!

A flea life cycle takes between 2 weeks and 8 months, depending on the temperature, their access to food, and the type of flea. They prefer a temperature of 70 to 85 F and a humidity of 70%. There are four stages in the flea life cycle.

  1. Eggs. A female flea lays 15 to 20 eggs per day on her host's fur. These often fall out while your pet is sleeping or walking. These eggs are white, smooth, and oval-shaped, about 1/50th of an inch long. 
  2. Larvae. In 2 to 14 days, the eggs hatch into larvae that look like tiny clear maggots. The larval stage can last 1 week to several months. Flea larvae will eat dandruff and skin flakes but also blood and feces (poop) given to them by adult fleas. The adult fleas poop out excess dried blood in tiny pellets, called "flea dirt." Eating the flea dirt turns the larvae from a clear color to nearly purple. Although blind and legless, they move quite fast and will live in floor cracks or under pet beds and carpets as they mature.
  3. Pupae. Hidden from view, the larva spins a white silken cocoon and molts into a pupa. This may take 7 to 10 days, but adult fleas may stay as pupae for months if it's winter. Once the weather turns warm and humid, they'll emerge as adult fleas ready to leave their cocoons.
  4. Adult fleas. Warm weather and the presence of an animal will encourage adult fleas to emerge from their cocoons and jump onto a host. A newly emerged flea can live up to a week without having a blood meal. Under ideal conditions, a flea can live up to 18 months, but a more normal life cycle is 2 or 3 months. 

photo of flea life cycle

Although it may be tough, you can see signs of a flea infestation in your home. Look for tiny black dots on your pets, furniture, rugs, carpets, or pet bedding. 

Also, check whether your pet is constantly scratching itself. That's a good sign that it may have fleas. 


If you have a pet, it's wise to know the signs that it may have a flea problem. They include:

Your dog (or cat) is scratching. Even if you don’t catch fleas red-handed, if you see your pet scratching or biting at its fur, fleas may well be the culprit. 

You can see them. Adult fleas are tiny, about 1/8th inch long. They're hard to see without a microscope (though it’s easier on light-colored fur), but they do have big back legs. For every flea you do see, there may be at least 100 younger ones that you don't. 

You can see what they leave behind. It’s called “flea dirt,” and it looks like pepper. You can spot it on your pet’s skin, or your pet could leave it someplace, like:

  • Its bedding
  • The carpet
  • That favorite chair they have been sleeping on, even though you’ve ushered them off it a thousand times

You can see their eggs around your home. These tiny white ovals will likely fall off your pet and onto your bed, the dog bed, the carpet, or that favorite chair, only to hatch a few days later into flea larvae.

You see tapeworms. These internal parasites look like small pieces of rice. They often slip out of your pet’s rectum (where poop comes out). 

Your dog (or cat) is losing its hair. It’s not from the fleas themselves, but from all the itching and biting. Fleas often gather at the neck and shoulder blades of your pet, where animals bite or scratch to get at them. The base of the tail and along the back of the legs is a favorite hangout for them, too. You may see fleas in the bare areas of your pet’s belly, too.

Their skin looks irritated. If you can get past your pet’s fur and look at the skin, fleabites are usually small, raised red dots. Again, look for bites on the back and neck and on the base of the tail.

Their gums are pale. Some pets with fleas (especially smaller kittens or pups) could get anemia, or a loss of red blood cells. Fleas can take in up to 15 times their body weight in blood. Pale gums often signal anemia.

Fleas on dogs

Although you may see fleas or fleabites on your dogs, flea eggs are harder to find, as they're microscopic, white, and may look like dry skin or sand. It's easier to spot flea eggs in your pet's bedding. You may see flea dirt there as well. Look for a salt-and-pepper mixture. 

You can also have your dog stand on a white piece of paper or in a white bathtub and comb its fur. Fleas and flea dirt will either be caught in the comb or fall onto the white surface.

Fleas on cats

The same signs of fleas on dogs also apply to cats. A flea-infested cat will bite or scratch itself a lot. And because cats have sharp claws, you might see sores on its skin from all that scratching.

Check your cat's neck or tail base, as these are spots cats can't groom easily, so fleas make themselves comfortable. You might also find flea dirt and flea eggs on them or their bedding.

You use the same comb trick to check for fleas on cats. Have your feline stand on a white piece of paper or white pillowcase and run a comb through its fur. 

Fleas on humans

Fleas don't live on humans because we don't have any fur where they can hide. But they will bite you if no animal is around. Technically, they're not biting as they have no teeth – they use their mouth part to pierce your skin and suck your blood.

You're most likely to get a fleabite on your ankles, feet, or calves, rarely on higher parts of your body, unless you happen to be sitting in a flea-infested area. 

If a flea bites you, you're likely to get a small itchy bump, circled by a discolored ring or halo. You may also see a cluster or line of bumps. The saliva that a flea leaves behind is an allergen. Your body sends a chemical called histamine to the area where the flea bit you to remove it. That's what causes the bitten area to swell and itch.

In severe cases, you might also get:

  • An allergic reaction (shortness of breath, hives) 
  • An infection from a disease carried by the flea (fever, headache, body aches, rashes, etc.)

If you've been bitten by a flea, you can treat the bites yourself with:

  • An antihistamine. A pill or cream containing a drug to counter the effects of histamine
  • Hydrocortisone. A steroid cream to reduce swelling and itching
  • Ice. Apply an ice pack covered in a towel for 10 minutes at the sore spot to reduce swelling and pain.
  • Aloe vera. Rub the gel from its leaves on your sore spot. It can reduce itching and pain.

Talk to your veterinarian about the best way to control your pet's fleas. They can suggest an insecticide, shampoo, spray, spot treatment, pills, or a liquid formula that can help.

Be sure to follow the product instructions. If you're using a pesticide, wear gloves. Don't let your pet lick off the pesticide after you apply it. Don't use a dog product on a cat, or vice versa.

Flea allergy dermatitis

Some people have a more severe response to flea saliva. If you have this condition, called fleabite hypersensitivity or flea allergy dermatitis, your skin may itch, swell, and redden around each fleabite. Pets can have this response, too. 






Fleas can carry dangerous diseases and transmit them to you and your pets. Among them are:

  • Plague. Rats and rodents transmit this disease to people who get it from handling an infected animal. Symptoms include fever, aches and chills, low blood pressure, weakness, shortness of breath, and nausea/vomiting.
  • Endemic murine typhus. Infected fleas transmit this through flea poop, which usually enters the skin when you scratch a fleabite. Symptoms include headache, joint/muscle pain, fever/chills, and nausea/vomiting.
  • Cat scratch disease. This is passed on to humans when cats scratch or bite them. Cats get the infection from fleabites or from fights with other cats that have the disease. Symptoms include a small discolored blister near the scratch, swelling, painful lymph nodes, fever, night sweats, and weight loss. 
  • Tapeworms. Tapeworm larvae as well as the larvae of other parasites may infect fleas. Infected fleas may spread these parasites to animals that swallow them while grooming themselves. Sometimes a child – or, rarely, an adult – accidentally swallows a parasite. Symptoms of parasites include nausea, weakness, stomach pain, dizziness/headaches, and weight loss. 
  • Canine bartonellosis. This is the dog version of cat scratch fever. Fleas carry the bacteria bartonella and spread it to dogs by fleabites. Occasionally, humans get it from dog bites. Symptoms in dogs include fever, swollen lymph nodes, sore muscles, nose discharge, a hard time breathing, vomiting/diarrhea, and coughing.
  • Anemia. Blood loss from fleas can cause animals to become very weak. Anemia (the loss of red blood cells) is more likely to affect kittens and puppies (particularly those that live outdoors) because they're smaller. Symptoms include pale gums, vomiting, a lack of interest in food, and weakness when they stand. 


Here how to treat your home for fleas:

  • Vacuum regularly the areas where your pet sleeps, sits, and eats, like floors, rugs, furniture, and pet beds. This will pick up fleas, flea dirt, larvae, and flea eggs. Don't forget baseboards and under furniture where fleas like to hide. Toss out the vacuum bag when you're finished.
  • Wash all pet bedding in hot water weekly and dry it in a hot dryer, if you can.
  • Steam-clean and shampoo carpets, rugs, and furniture. If you notice fleas after doing this (they may hatch because of the warm water), keep vacuuming and cleaning until they are gone.
  • Spray the house with a hand sprayer, or in severe cases, use a flea bomb or room fogger. Remove family members and pets from the affected area(s) when using insecticides and follow the label directions closely.



The best way to deal with a flea problem is to prevent it. Follow these strategies:

  • Regularly give your pet a pill to prevent fleas. Your vet can help you pick the right one.
  • Have your dog or cat wear a flea collar. Check with your vet before combining a flea collar with flea medication.
  • Thoroughly vacuum areas where your pets live or sleep, including floors, carpets, and pet beds. Regular vacuuming can remove up to 95% of the flea eggs, as well as some larvae, and adults.
  • Groom your pets regularly.
  • Outside, treat kennels and dog runs with granular products as opposed to sprays. They work better.
  • Remove debris and low-hanging trees and vegetation to reduce fleas. Cut tall grass.
  • Seal crawl spaces, areas under porches, and openings to basements, where pets and wild animals like to hide. 
  • Consider keeping your pets from roaming outdoors, where they're more likely to come into contact with fleas. 

Once you've killed the fleas on your pet through medication and grooming, keep them from returning by thoroughly cleaning and vacuuming the areas where your pet lives and sleeps. If your dog or cat goes outside, you'll need to do some outdoor maintenance as well. 

Here are some frequently asked questions about fleas:

 What kills fleas on pets instantly?

  • Shampoo your pet and/or give it an over-the-counter flea treatment. Some products are labeled to work in as little as 30 minutes.
  • Can humans catch fleas from pets?

    Yes, they can. Fleas won't live on you, but they will bite you if you're close enough.

  • What can I do if my pet has fleas?

    Your veterinarian can give your pet a pill to treat the fleas. Then, shampoo your pet to get the fleas out of its fur. Get a flea collar for your dog or cat to wear. To prevent fleas from returning, regularly vacuum and clean the areas in your house where your pet likes to go.