Why is my dog suddenly aggressive or naughty? 5 reasons why…

December 09, 2022
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So you have been doing amazingly with your dog training but suddenly your dog is being naughty again, or even aggressive.

It’s SO disheartening, you have done everything right and have worked so hard so why do you now have a devil dog on your hands?

Firstly, stop blaming yourself!  You are doing your best and it’s most likely that the reason isn’t down to anything that you have or haven’t done.

In this blog I will outline 5 possible reasons:

1. My dog has suddenly become aggressive or naughty because they are a teenager!

Dog training why is my dog misbehaving all of a sudden
Why is my dog misbehaving all of a sudden

This is sooooo common and with proper training and TIME it will get better – so don’t despair.

Our dogs enter adolescence at around 6 to12 months and can end anywhere from 18 to 24 months old.

Imagine that your dog is living wild within a family group.  As a puppy it is completely reliant on the family group for its survival, however as it become sexually mature it needs to make the decision as to what is the best way to ensure it’s genetic line is continued for generations to come.  

So it has two choices.  

Either stay within the family group and help to bring up the puppies of the parents


Go and find a mate and establish its own family group.

So it will test the boundaries – just like human adolescents.

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Adolescent rebel dogs

All that puppy training you did seems to go out of the window.

Recall – gone.

Loose lead – gone.

Focus – gone.

And the really annoying thing is that often your dog will listen to other people but not to you.


And it’s totally natural, but that doesn’t mean we can’t or shouldn’t do anything about it.  If we don’t the problems are likely to continue.

Our reactive rebels one to one programme can be done in person in your home, or online via zoom so wherever you are based, check it out here and book a call!

2. Why has my female dog’s behaviour suddenly deteriorated?  She is around 6 months old

It could be that your dog has come into season – hormones everywhere!

With some dogs it can be difficult to tell when they come into season if they are particularly vigilant about cleaning themselves as some bleed more than others, so you may not always notice bleeding.

The worst time from a behavioural point of view is towards the end of the season and afterwards when progesterone levels are high.  This lasts for around 9 weeks before the behavioural issues will start to subside.

If you are going to have your female dog neutered speak to your vet and make sure you do not spay until progesterone levels are back down to a normal level.

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3. Why has my female dog’s behaviour suddenly deteriorated?  Her season was around about 6 weeks ago.

Female dogs can have phantom pregnancies which start around 6 weeks after a season has finished.  Their appetite can reduce and reactivity and resource guarding can increase.

See your vet!

4. My dog has suddenly become naughty and none of the above are right!

The cause may be pain, itchiness or discomfort. 

Take a look at your dog’s poo!  Great, eh?  Are there any changes?  Are stools loose?  

How is your dog moving?  It is worth videoing their movement in slow motion.

Are they scratching more than a couple of times per hour?

They could have a skin problem.  They could be in pain.  It could be a gastro-intestinal problem.  

Here’s the thing, pain leads to stress which can lead GI problems and diarrhea and vice versa. 

The only person who will be able to tell you what’s wrong is your vet so get a vet check and take with you any observations and videos you have made to help them.  Sometimes a behavioural change is the first indication of a medical problem.

However, some physical signs can be as a result of stress so check out our one to one programmes here to help.

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Better safe than sorry!

 5. I have had a vet check and it’s all clear!

So the behavioural change could be down to stress, fear or anxiety.

Check out our one to one programmes here which can be done in person or online so distance is not a barrier.

If you’d like a chat about your dog’s behaviour, book a call here.

I’d LOVE to see you in my Facebook group!  Click here to find out how to join.

How to calm a reactive dog.

Your best option is to get the support of a dog behaviour specialist. Go for someone who uses science based positive reinforcement methods so you can get to the heart of the problem rather than the quick fixes offered by so called “balanced” trainers.

I’d love to help, to book a free call just click here: Free call to discuss your reactive dog

To join out online reactive dog membership click here: Online reactive dog membership

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