How to reintroduce cats after redirected aggression and hissing?

This may be difficult to correct but it generally can be done. Continue using the diffuser. Try switching litter boxes, beds, and rubbing each cat with the same towel to try to get them to smell like each other. Here are some links which may be helpful: https://www.petcoach.co/article/7-ways-to-calm-an-anxious-cat/ https://www.petcoach.co/article/bringing-home-a-new-cat-or-kitten/ Here is a great article about cat's instinctual needs: https://www.petcoach.co/article/why-every-cat-needs-a-place-to-climb/ Setting aside 30 minutes a day for vigorous play for both cats or switching the food to Royal Canin Calm may help. The veterinarian can also prescribe medications which can help with aggression. I hope this helps and please feel free to post any additional questions.

Oh no, that's not good! I would separate the cats, and slowly reintroduce them to each other. Take the cat who is aggressive, and put her in her own room with her own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let the other cat in the aggressive cat's room while the aggressive cat is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove the second cat from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let the aggressive cat out of her room, and see how she interacts with the other cat. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep the cat in her room when you go out until they are comfortable with each other. I hope this helps!

Thanks for using PetCaoch! It’s not uncommon to hear about behavior like Alyssa. It can take a lot of time and patience for them to get along but here are some tips for decreasing stress for Alyssa in the short term. -Feliway- calming cat pheromone- comes in many forms from pet stores or online. 

 - Adding a litter box. Studies show that the ideal number of litter boxes for a home is #of cats +1 . This is regardless of how clean you keep his current litter box. 

- making sure she has plenty of “high space”. The safest (and therefore least anxiety-inducing) place for a cat is up. If you don’t already, get a cat tree or put up a shelf or two that she can go perch on. 
 Feeding them in separate rooms with two or three water bowls throughout the home is also a good idea as perceived competition for resources is a common problem in cats. Best of luck to you and your kitties!

You could start by feeding them on each side of the door that separates them so they can smell each other and have it be a positive experience. Next, you can switch rooms - lock your cat in her room so your cat can investigate the smell of her cat and let her cat roam the house. Then you can try them together while you can supervise and see what happens. You could get some Feliway spray or a diffuser and use that to alleviate any stress/anxiety.

I would try a Feliway spray, diffuser or collar. It is a pheromone that helps with relaxation and anxiety. There are also supplements for anxiety. Set up separate areas for feeding and two litter boxes so they each have their own space with an area that they both have access to. Usually over time they will adjust if left alone. If she’s still aggressive there are prescription medications to give her for a little while to help her adjust so please discuss this with your veterinarian. Thanks for using Petco Pet Education Center, formerly Petcoach to help you care for Kaji.

Getting a new kitten into the house is stressful for the existing cat, and that is likely why Luna is acting this way. I would slowly introduce them to each other. Take Odie, and put him in his own room with his own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let Luna in Odie's room while he is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove Luna from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let Odie out of his room, and see how he interacts with Luna. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep Odie in his room when you go out until they are comfortable with each other. I hope this helps!

Separate Lilly from the kitten for a few days. Gradually reintroduce them. Start with a closed door between them so they can hear and smell each other. Progress to seeing each other but without physical contact. Once they are acclimated, try short periods of supervised contact. Use a pheromone prodcut such as Feliway Spray or the plug in diffuser to decrease any anxiety or aggression.