WHY IS YOUR DOG SUDDENLY AGGRESSIVE?

The biggest fear of all dog owners, their dog has turned into an aggressive dog.
Some of the most typical reasons aggression's in dogs occur is through a trigger, may it be a strange dog, a bike, a loud child or simply by yelling at the dog. Dog owners with aggressive dogs start to ask themselves what did they do wrong in the training or when did the symptoms first occur.

Possible reasons for a sudden aggression:

1. A puppy who was allowed to do everything with minimal rules. The times he growled and showed his teeth as a puppy was a laughing matter and he looked so cute while doing so. A year later it has turned into a problem because no one addressed the issue while he was a puppy.
2. A health issue. Sometimes pain or an illness can cause the aggression.
3. A dog who comes from the shelter. We don't really know what the dog has been through in the past, the shelter workers try to only tell about his positive attributes so that he will find a home as soon as possible. For an example, there has been many stories about shelter dogs brought home who suddenly turned aggressive and bit the new owners or their children.
4. Not getting enough exercise. A dog that has been cooped up inside an apartment, only getting out a few times a day for short walks, can be very prone to get aggression's. The dogs cannot sometimes control themselves when they are getting over excited.
5. The dog breed (remember, not in all cases!). If you have a Pitbull he will usually be more of a risk than a mini Poodle. Not only because of the type of breed, but because of the size and strength of these types of breeds. We shouldn't forget that they are still being bred today for dog fighting, but mostly it is important how he is socialized and trained as a puppy/young dog. 
6. The experiences the dog has had. If well socialized as a puppy, without bad experiences, you will usually have a great dog in the end. If your dog has a bad experience as an older dog, it can also affect his behavior.
7. Food aggression. Food aggression is a typical kind of aggression in dogs which is only a natural behavior they have from their ancestors, the wolves. If you have ever watched a video of wolves eating, there is a clear ritual, the alpha wolves (in most groups these are the parent wolves) eat first and they like to protect their prey in a certain way which reminds very much of dogs with food aggression's. They growl, show their teeth and put their both front paws in between their food. We just don't want our dogs to protect their food. Again, it's important how you treated the feeding time with your dog as a puppy, did he have to wait until you told him "go ahead", did you sometimes take the bowl away or put your hand in the bowl? All these things are crucial while training your dog not to be aggressive around food.
8. Learned behavior. In most cases the dogs who show aggression, may it be fear related or any other reason, only do it because it's a learned behavior and because it's completely carved in his memory it's so hard to get rid of it. Did you just let it happen time after time not addressing the problem?
9. Your reactions to the aggressive behavior. How did you react when your dog showed aggression for the first time? Did you pet him because it looked like he was scared and you wanted to show him you are protecting him? Did you scream at him? Did you get nervous and frightened? This is so important to reflect on because your dog is usually showing the same feelings you are. If you are nervous, your dog can feel it even through the leash and he will automatically become nervous as well. Also if you pet him while doing an unwanted behavior, you are rewarding him and he will expect the next time another reward when he shows aggression's. If you scream at your dog, your dog will feel your frustration and the anger in your voice that he sometimes starts to ignore you completely and decides to do whatever he feels like or he will get even more riled up.

What can you do if your dog has suddenly turned aggressive:

1. Make an appointment at the vet and make a complete check up. In many cases the dog might have internal pain which might be causing the aggressive behavior.
2. Call up a few reputable dog schools and explain about your situation. Find a good dog school where you can do private sessions with dog trainers especially educated and trained in dog aggression.
3. Find a way to avoid the aggression triggers the best you can. For an example, if your dog is aggressive towards other dogs, cross the street if you see a dog coming towards you.
4. After avoiding for a while and when it's working well you can start with the next step. Now you can slowly introduce the triggers again, but very slowly. Best would be to use a helping person for this step.
Start at a very long distance and go very slowly closer to the trigger. While doing so, reward him for good behavior. You will see when you have gone too far, step back and try again (immediately or the next day) to get closer to the trigger. Never punish your dog for a setback. If he starts showing aggressive behavior just ignore it, don't pet him or talk to him if it happens, just step back, and know that you went too close to the trigger. Do these exercises all the while rewarding with a toy (best is to use a fun squeaky toy to get your dogs attention) or yummy treats (use something your dog cannot resist, like cheese or hot dogs).
Do the exercises as often as possible for a longer period of time. Some dogs need longer than the others. Finally when you reach your trigger, it would be good to use a muzzle in the first time, just as a precaution.
5. Always stay calm, never scream at him instead talk in a lower region voice in a calm way and show him you are the leader with your confidence.
6. You will need very much patience and training for it to work but don't give up or get frustrated if it doesn't work immediately, you will be rewarded in the end.

** All based on my own knowledge and experiences in training dogs. **