You have probably noticed your cat’s mouth randomly hanging open from time to time.

While it can be entertaining to say the least, it is usually not random at all.

There are actually a variety of reasons for this amusing and seemingly eccentric behavior.

1. The Flehman Reaction

The “Flehman reaction” refers to the reaction a cat sometimes has when it smells something interesting. This is likely the result of the animal inhaling certain types of pheromones. While it is unclear how exactly cats interpret the message these pheromones communicate to them, it is an interest reaction to say the least.

This reaction is commonly associated with inhaling a very strong smell of some kind. It often observed in cats when sniffing their owner’s feet. A lot of people’s feet give off a very pungent aroma, which these animals can easily pick up.

2. Health Issues

Another reason that your cat’s mouth hangs open could be that it has some sort of medical condition or health problem. 

3. Nasal Blockage

There are a number of different things that can cause nasal blockage, including allergies and bacterial infections. Both of these things can clog the nasal passages, which forces the cat to breathe through its mouth.

While it is fairly uncommon for cats to have seasonal allergies, it does happen. Your cat’s allergies might also be triggered if you aren’t very good about cleaning your home. If there is a lot of dust nearby, it could mess with their allergies. You will probably also notice them sneezing and/or coughing if this is the case.

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Even a tumor in your cat’s nasal passageway can cause them to keep their mouth open. While it is a less common explanation than allergies or an infection, it is still possible.

kitten mouth open

4. Asthma

Believe it or not some, some cats actually suffer from asthma. In fact, about five percent of felines have this condition. While no cure exists for asthma, your veterinarian can prescribe medication to keep it under control.

If your cat’s asthma goes unchecked, it could be fatal. The most common and most noticeable symptom of this is labored breathing. If it looks like your cat is having a difficult time breathing properly, this could be the cause. You’ll want to take them to the vet so they can provide you with a proper diagnosis.

5. Mouth Pain

If your cat is experiencing any tooth or gum pain, they may keep their mouth open to avoid additional discomfort. There are all sorts of dental issues these animals can develop. You should check your cat’s mouth for swelling of the gums, which can indicate gingivitis (gum disease).

Some of the telltale signs of dental problems in cats also include bad breath and not eating. If your cat is experiencing any mouth pain, they might be avoiding eating because it hurts too much.

6. Obesity

Cats that are severely overweight may start to breathe through their mouths. They do this to take in more air as a way of compensating for the additional strain on their body. 

It is important that you help your cat maintain a healthy weight. This means feeding it healthy cat food and keeping treats to a minimum. You also need to make sure that they get plenty of exercise on a daily basis.

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If your cat lies around the house most of the time, you might want to try taking it for a walk. Not all cats respond well to being put on a leash, but it is worth trying. This can be a good way to reduce your cat’s weight, which will improve its overall health.

cat suprised

7. Calicivirus

Calicivirus or FVC is an infection that affects the respiratory tract in cats. This can cause problems with breathing and other serious symptoms if it is left untreated. It is also characterized by ulcers on the tongue, nasal discharge, and loss of appetite.

It is crucial that you get your cat to the vet if you notice these symptoms. If this is caused by a bacterial infection, your vet will most likely prescribe powerful antibiotics. Further treatment may be required. 

There is also a chance that your cat will need to stay at the hospital for treatment and observation for a few days.

8. Heatstroke

Cats don’t do very well with being out in very hot weather for long periods of time. This is because their skin is so incredibly thin. It is important that you keep your kitty hydrated when it is hot. They may start panting if they become dehydrated.

Heatstroke can quickly become serious, so you will need to look out for these signs. You should try to limit the amount of time that your cat spends in the sun. While they might enjoy it, moderation is the key.

9. Unpleasant Taste

Your cat’s mouth might start hanging open if they taste something they don’t like. This could be a new food you bought them or some random thing they licked.

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If you notice your cat eating or even licking anything that is toxic to them, it is important that you get them to the veterinarian right away. The longer you wait to do this, the more danger they are going to be in.


  • The Flehman Reaction is the name for when a cat opens its mouth and eyes wide after smelling something “interesting”.
  • A nasal blockage that is due to allergies, a foreign body or respiratory infection could cause your cat’s mouth to hang open.
  • If your cat is severely overweight, it could start breathing through its mouth to compensate for the extra strain being put on its body.
  • Gum or tooth pain can be a common cause of this behavior in cats. Look for swelling of the gums to determine if this might be the cause.
  • While not many cats have asthma, it is a possible explanation for this behavior.
  • Your cat’s mouth could be hanging open because it smelled something it didn’t like.
  • Cats that are suffering from heatstroke might open their mouths and begin panting due to dehydration.
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Hi! I'm Anna and I´m a certified cynologist (KAU, ACW). Expert, blue cross volunteer, owner of Chinese crested kennel "Salvador Dali" and breedless friend called Fenya. "I can't imagine my life without dogs and I totally support the idea #AdoptDontShop".