What are the Reasons for Sudden Aggression in an Older Dog?

What are the reasons for sudden aggression in an older dog

Your previously sweet and loving senior pup who literally wouldn’t hurt a fly, seems to have gone demonic overnight. Don’t worry because there are reasons for sudden aggression in an older dog.

What does this aggression look like for you?

Has she started snapping? Snarling? Nipping? Biting?

In what situations have you noticed this aggressive behavior?

It’s a good idea to take notes every time you see your dog become aggressive, and if there are other people in the household, ask them to do the same. When you see them on paper a pattern may start to emerge of what’s going on at the time. It will definitely help with a diagnosis.  

What causes sudden aggression in dogs?

Pain or discomfort

Pain is a major reason for dog aggression and can be due to arthritis and other joint issues, dental disease, recovery from surgery and pancreatitis to name just a few.

Signs a dog is in pain

  • Aggression/lashing out
  • Whining or whimpering
  • Clinginess
  • Lack of interest in things he used to enjoy
  • Reluctant to go for walks/unable to walk
  • Lethargy
  • Difficulty sleeping or resting
  • Licking one spot on his body
  • Difficulty getting up and lying down
  • Pawing at his mouth
  • Drooling


Dogs may experience an increase in anxiety as they age, and that anxiety can sometimes translate into aggression towards their humans, other pets in the family, strangers…anyone really.

Dementia in a dog

Confusion, anxiety and not recognising the familiar are just some of the symptoms associated with dementia, and yes that can lead to an otherwise sweet natured dog displaying bouts of aggression.

Vision and/or hearing loss

Imagine how scary it must be for your dog as she starts to lose her hearing, vision or both. She has no idea what’s going on, and because she is startled more easily may lash out before she realises who’s approaching.

If this is the source of aggression, I assume you’ve already taken her to the vet and/or eye specialist and the situation, at least medically, is under control. Making adjustments to accommodate these changes can also help, and here are a few easy fixes –

  • Make your presence known before touching her by calling her name, stomping on the floor…
  • Don’t move furniture around
  • Keep the floors clutter free so she doesn’t trip, hurt herself and become anxious
  • Try and keep the noise and activity level down for a bit

Brain tumor

Not common but not unheard of, a mass on the brain can cause a sudden change in personality.

A new pet

Your oldie may be very content with the life she has, and has little patience or interest in interlopers. You may have decided to bring a new pet into the family with the best of intentions, but now the newest addition is bothering the long time resident and she’s not liking it. This may very well cause some aggression, so speak to a dog trainer to help you figure out the way forward.

What are the Reasons for Sudden Aggression in an Older Dog

How to stop aggressive behavior in dogs

Take your dog to the vet

Whenever there is a change in behavior, particularly in old dogs, I always recommend a trip to the vet, because there is the likelihood a health issue is starting to rear its ugly head. Your vet will probably recommend blood and urine tests to help with a diagnosis. Once you have an explanation for this aggressive behavior, a treatment plan can be drawn up to help.

Be aware of what induces aggression

Being aware of the situations that induce aggression means there are things you can do to prevent or minimize them. 

Joint pain

If joint pain is making it hard or impossible to walk, there are plenty of mobility aids that can help –

  • harness
  • pet stroller
  • ramp
  • mats on slippery floors

Check out this article “Mobility Aids for Dogs” for more detailed information. 

Too much commotion in the house

If the kids are home for the summer, you have a big event going on or whatever the reason your house has become more chaotic than usual, create a safe and quiet space your pup can retreat to. You don’t want to banish her to a back bedroom all by herself, but set up a bed there anyway in case that’s where she wants to be.

A crate in the corner of where the action is can be an option as well. Leave the door open, put a nice comfy bed and blanket in there and cover a couple of sides to give her privacy. Have options and she’ll choose where she wants to be.

One more thing – she may prefer a room out of the way, but you don’t want her spending all her time alone there. Try and calm things down when possible so she can be with the rest of the family.

Get everyone involved

Let everyone in your household know what’s going on, and together come up with strategies to help your dog. 

Play calming music

A sanity saver for me was a CD called “Through a Dog’s Ear.” Although my dog did not have aggression issues, she became quite anxious after her dementia diagnosis and this particular CD calmed her down like no other could. You can find a 13 minute sampler on YouTube before buying to see if it works. Here is a review I wrote about it that will give you more information. 

Sudden aggression in an older dog – conclusion

I hope this information about sudden aggression in an older dog has made you feel better, knowing there is action you can take that will help you figure this out.


Have you been able to determine why your senior dog has suddenly become aggressive? What was the cause and how have you been treating it? Sharing helps others so please leave a comment below.


Hindy Pearson
I am a dog trainer and behaviour consultant, specialising in working with first time dog owners. Whether you're thinking of getting a dog and aren't sure if it's the right time, or you've been sharing your life with one for awhile but there are issues you can't resolve, I am here for you. No matter where in the world you live I can help.


  1. Ruth Epstein

    Great post and with Layla aging I have noticed some changes with her but no aggression thank goodness but I am monitoring her behavior all the time. Her newest is fear of the dog park but am working on that by going into it from another entrance and sitting away from all the dogs and it seems to relax her more.

    1. Hindy Pearson (Post author)

      I know you watch Layla so closely, she’s a lucky pup! That’s a great idea going in from a different entrance and sitting at a distance. She still gets to enjoy the sights and sounds, but she’s calmer.

  2. Michelle & The Paw Pack

    Very informative post. My older dog is usually the sweetest boy ever. A few years ago, seemingly out of no where, he started hiding a lot. When I tried to cox him out of his hiding spot for the first time ever he snapped at me. I knew right away that something was off and made an appointment to see his vet. It turned out that he had arthritis pain in his hips and probably wasn’t feeling very well. We got his arthritis pain well managed and he instantly went back to his happy, sweet self. I’m so glad I knew enough to realize that he wasn’t just being aggressive for no reason, it was a sign of something else going on.

    1. Hindy Pearson (Post author)

      He’s so lucky you realised something wasn’t right and took action. He’s lucky to have you, and it’s great to hear he went back to being his happy self. I’m constantly banging on about paying attention to changes and taking dogs to the vet, rather than assuming it’s all part of aging and leaving things be.

  3. Sadie

    I have been concerned about Henry after recently losing his sister. He seems quite depressed. At eleven-years-old, his eyesight is declining. We would like to rescue another, younger dog and I worry about his reaction. Of course, we’ll arrange a ‘meet and greet.’ Hoping it goes well and he welcomes his new sister. He does seem to enjoy a larger pack. Thank you for this informative post.

    1. Hindy Pearson (Post author)

      It’s definitely tough figuring out if a new dog is the right move. A younger dog that’s boisterous can either help him have fun again, or just be an annoyance. A meet and greet or even a foster situation is a great way to go.

  4. Lola The Rescued Cat

    This is great information. I especially like the reminder that people should be mindful of too much commotion. That’s also good info for older cats. When I had a senior cat and had family holiday dinners, I made her a special place in the bedroom so no one would bother her.

    1. Hindy Pearson (Post author)

      A lot of the information is definitely relevant to cats as well. I bet she appreciated the sanctuary away from the noise and crowds!

  5. Jana Rade

    Most likely, pain. Or other health issues. Thank you for bringing this up to people’s attention.

    1. Hindy Pearson (Post author)

      Absolutely right, unfortunately many assume changes are just part of the natural aging process.

  6. Sweet Purrfections

    I always appreciate your posts about senior dogs. I’m watching my mom’s dog closely as he moves through his senior years.

    1. Hindy Pearson (Post author)

      Thank you, that’s so kind of you to say. Anything I can do to help, please let me know.

  7. The Dash Kitten Crew

    Being aware of what causes or triggers aggression is something every dog parent needs to be aware of. Older dogs (and cats) change their behaviour as they age and this needs to be taken into account every day, If you are clueless about causes monitor day by day and take notes – it will help you and your dog so much if you can act positively to ensure they age well and happily.

    1. Hindy Pearson (Post author)

      Well said! I wish more people realised there are reasons for sudden behaviour changes and they should be investigated. Sadly too many react and leave them in a shelter because they think they’ve become nasty and they don’t know how to deal with it.

  8. Beth

    A friend of the family had a senior Maltese who was losing a battle against kidney and heart failure. If he was startled, he would snap and bite. My mom likened him a moray eel. Thankfully he was in a quiet household, and they were able to figure out how to get his attention without scaring him.

    1. Hindy Pearson (Post author)

      Poor baby so sad, but it is good news he lived in a peaceful home and his guardians were able to figure out the best (and safest way) to communicate. He’s lucky to have had such an amazing family.

  9. Dorothy "FiveSibesMom"

    As always, another great post, Hindy! My furangel Chelsey had developed some sudden outbursts of aggression at age 13, and it was due to dementia. Unfortunately, at the time there was not much info about it and it took a long time before we realized what was happening to her. I also had two Husky pups who just joined the family and she would go from romping and playing to suddenly chasing them down like prey. At first, I thought it was due to her age and maybe she just suddenly got annoyed, so I separated her from them and let her spend her days in the house where she chose my daughter’s room, laying in the sunbeams from the window, or in her laundry pile! As her symptoms became more – I started thinking dementia…and she finally, heartbreakingly came to the point where we had to help her go as she was becoming so unaware, biting my daughter (her very best friend), biting doors (and literally tearing it off and chewing it up that the gnarled metal looked like the Hulk ripped it off), to pacing, staring off into corners, licking the rug, and you could see in her eyes, my sweet girl was gone. I know we share that heartbreak of dementia… but that was the reason for her aggression. I am fortunate that now that the Husky puppy who is now a 14 year old (oh where does time go?) and is deaf and has an issue with her one eyes, had adjust well and is sweet and follows my lead. I really thought she would become aggressive, but she is a sweetheart! Pinning your post to share with others!

    1. Hindy Pearson (Post author)

      Thank you Dorothy, that is so kind of you to say, and thanks for pinning. Yes we definitely do share that heartbreak, and I can’t imagine how tough it was for you to see Chelsey go through those changes, not knowing what was going on. I’m finding between my experience and those of so many other senior dog parents, too many vets aren’t much help when it comes to dementia, many not even mentioning it as a possible explanation. Obviously you did the best thing for her, as heartbreaking as it was, but like you said you knew it wasn’t Chelsey anymore. Dogs really do adjust well and I’m glad to hear the puppy is doing well.


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