14 min

Why Do Cats Hiss At New Kittens Or Cats?

If you notice some hostility between a new kitten and your resident cat, you might be wondering why. Read on to learn how you can help keep the peace.

Bridget Reed

Updated November 10, 2022 • Published October 27, 2021

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Why Do Cats Hiss At New Kittens Or Cats?

Getting a new kitten is exciting for everyone,  but perhaps not for the cat who has lived with you longer. If you recently brought a new cat home and realized that your older cat is hissing or growling at your latest addition, it is time to intervene for both of the cats’ sakes. You might consider hissing one of the signs of aggression, but the reality is that it’s more complicated than that. Your first step is to figure out why your cats are not getting along.

There are several reasons why these cats might not be getting along. Getting to the bottom of it will be helpful in piecing together how you can create harmony between the two pets. 

In addition, you will learn more about how you can properly calm your older cat. It’s important that boundaries are created so that both the older and younger cats feel respected and safe.

Lastly, if you have not yet introduced the two animals, you should take steps to ensure that you do this correctly. The initial introduction between two cats can make a tremendous difference in how they perceive each other moving forward, so be cognizant of that. 

Why aren’t my cats getting along?

The reality is that oftentimes, even if your adult cat is friendly, they could have a difficult time getting acclimated to having a new kitten around. The adjustment is just as huge for the adult, older cat as it is for the young kitten. Treating both of your pets with understanding and patience will be useful in your journey ahead. 

While younger kittens are frequently eager to make friends, adult cats are sometimes more standoffish and settled. As a result, there is sometimes conflict between the two. Older cats can even act out if they are distressed that there is a new addition to their family.

Sometimes they will hiss, stop eating, or even act depressed. If you are concerned about the health of your older cat — or your kitten — you should seek veterinary attention. Pawp has a team of vets who are available whenever you need them, wherever you need them, so you can get your questions answered as soon as possible. 

Nevertheless, you might be confused why your older cat is hissing at a new addition to your family. Here are several reasons why your cats are having a difficult time getting along. 

Older cats don’t like change

Your older cat has settled in their routine, and as a result, sometimes older cats are averse to change. Generally speaking, cats do not enjoy change. This is especially prevalent when it has to do with their territory—but more on that later. 

As a result of the change, your older cat might be experiencing a tremendous amount of anxiety or is feeling misunderstood. In addition, finding ways to calm your older cat can help ease the tension that could accompany the arrival of your new kitten. 

They’re territorial

Cats are territorial creatures. As a result, your resident, older cat likely feels that an uninvited cat is invading their home. In most cases, the older cat thinks that they own your home and that a new kitten is a threat to that. 

Therefore, they can act out to assert dominance and stake claims on their territory. Luckily, there are preventative measures that you can take to ensure that the initial meeting between your pets is smooth. 

They miss being the center of attention

When you bring a new cat home, your old resident cat might feel that they will no longer be attended to. It’s essential that you prove to them that this is incorrect. In addition to defusing the competition for attention, you should also ensure the cats are not competing for food. 

You should anticipate spending time with both your resident cat and new kitten during this time. In addition, you should even invest additional time with your older cat to calm their anxiety. 

How can I calm my older cat?

As mentioned earlier, it’s entirely possible that your older cat will be anxious as a result of the arrival of a new kitten. There are steps that you can take to ease the nerves of your older cat. These can help smooth the transition for your resident pet. 

Use pheromones

Calming pheromones are useful to help ensure that your cat feels both safe and secure. These work by sending reassuring messages to the pet. During a period of transition when your cat feels their way of life has been upended, utilizing the power of pheromones to make an impact can be hugely helpful. 

These, of course, are not a magical solution, and you can consult your vet if you do not believe they are working for an alternative course of action. They could, however, provide your cat with a more calm foundation to work with. 

Try supplements

If you feel your cat is experiencing anxiety and pheromones do not seem to be working, you might consider trying a calming supplement to reduce their anxiety. If you need suggestions for these, you can ask a trusted veterinarian, and they will be able to point you in the right direction for your individual pet. 

Prepare your home

It is wise to prepare your home for your new feline addition about a week ahead of time. This is so your older cat can get used to these new supplies that are in the house. They will have time to get used to and smell everything. 

In addition, you should be sure that you have everything you will need for your new cat. It is better to be over-prepared than underprepared; if you are stressed about your new pet’s arrival, your older cat will be able to pick up on that anxiety and can absorb some of it. 

Also, designating a specific space such as a small room for the new kitten to spend their first week in is an effective tactic. The resident cat can go near the door of the room to smell the new kitten, but direct contact should be restricted. 

Give your new cat their own space

You will want to make sure that your resident cat does not feel their space is being overrun by the new cat. This is especially relevant when it comes to eating; you should not feed the animals in the same vicinity as each other to establish that there is no competition for food. 

Make sure your older cat is healthy (and vaccinated)

Unfortunately, kittens are prone to some diseases, and it’s important that if you are to have both of your cats live together in the same place, you are looking after the health of your older cat. 

In addition, your younger, new cat might not be able to get all of their shots until they have reached a certain age, which means your resident cat could be made vulnerable to diseases. To prevent this, make sure that your older cat is vaccinated. 

Have them spend time together

You cannot keep your cats separate forever, and nor should you. Eventually, your pets will have to spend time together. It’s critical that you are tactful about this, especially the first time.

After about a week, you can encourage the young cat to explore their new surroundings and encourage positive interaction between the two animals. Never force them, and provide praise and treats for positive behavior. 

Pawp veterinarian Dr. Laura Robinson says that “usually time will help” cats acclimate to each other. She recommends that cat owners “introduce (the cats to each other) for short periods at a time if possible” to create a healthy atmosphere.

Establish a hierarchy

Your final task is to establish a hierarchy in your home. Cats require order, and a hierarchy provides this. As a result, your older cat might try to establish this with the younger kitten. In some cases, this will mean that they swat or even hiss when the new cat does something that they do not approve of. 

This is normal, and as long as it’s just hissing and swatting and nothing more concerning, try your best not to interfere and allow the cats to work it out on their own accord.

The older cat is asserting their dominance, and the younger cat is learning all about boundaries. Cats have their unique way of communicating with each other, and it’s essential to respect that. 

Dr. Robinson lists a number of reasons why cats may hiss, including in warning of an attack, pain, “if they are stressed by something in their environment,” or if the play dynamics are too rough. 

How should I introduce my cats?

Introducing your cat requires time, patience, and careful preparation. Once your new cat is in a kitten-safe room that you prepared for them prior to their arrival for a while, and your cat has had the opportunity to get acclimated to their new supplies and their scent, you can begin the introduction. 

You can encourage an activity that they can do together. Be sure to be diligent in providing them with the same treats, water in different bowls, and feed them in different locations.

Introducing your cats isn’t always easy, but there are ways to make it easier

Introducing a new kitten to an older, established cat isn’t always easy, but it’s certainly possible with the right preparation and determination to make the two create a tolerance for each other.

While the two cats might not be the best of friends right away, you are aiming to ensure that they do not harm or hate each other. Take small steps and remember when they behave well to reward them with treats and praise.


Cat Research | TTU  

Introducing a New Cat | Cummings Veterinary Medical Center  

Feline Vaccines: Benefits and Risks | Cornell University  

Introducing Your New Cat to Your Other Household Cats | UC Davis Vet Med  

Even healthy cats act sick when their routine is disrupted | ScienceDaily

Feline Behavior Problems: Aggression | Cornell University

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