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Warning Signs and Causes of Dangerous and Aggressive Dogs

Adrienne is a certified dog trainer, former veterinary assistant, and author of the online dog training course "Brain Training for Dogs."

Do you know the warning signs of an aggressive or dangerous dog? Learn all about the warning signs in this article.

Do you know the warning signs of an aggressive or dangerous dog? Learn all about the warning signs in this article.

Dog Aggression Should Not Be Ignored

Sometimes, dogs display behaviors that are a far cry from what might be expected of ''man's best friend." The owners of such dogs might ignore or excuse those behaviors with phrases such as ''he'll grow out of it," ''it's just a phase,'' or ''he only does it every now and then."

Sugar-coating these issues, however, is not helpful. In fact, in many cases, these behaviors are likely to increase and escalate if they are not addressed.

Two Behaviors That Could Be Warning Signs

Growling and biting are two general behaviors that could indicate problems. Neither one should be ignored.

1. Growling

While some people appreciate growling because it indicates that the dog is warning them before biting, a growl should not be underestimated because it may indicate that the dog has a low-level threshold or is weak-nerved.

2. Biting

Biting is, of course, the most obvious act of aggression that dogs express. The bite does not have to break the skin to be considered a significant threat. Oftentimes, owners start seeking help once their dog has bit somebody, which is too late. In many cases, signs of increased aggression were ignored or may have been too subtle to be noticed by the inexperienced eye.

Warning Signs of Dog Aggression

It's important for owners to try to identify signs of aggression in their dogs early—ideally, before aggressive behavior escalates to biting.

  • They growl when eating.
  • They lift their lips and snarl while eating.
  • They get tense and tend to stop eating as you approach.
  • They growl when they are chewing a bone.
  • They steal food and get aggressive when you try to retrieve it.
  • They respond aggressively when they are found scavenging the trash. For more on this, read "Dog Resource Guarding."
  • They growl if forced off a bed or couch.
  • They growl if allowed on the bed and the owner moves too much.
  • They growl if awakened.
  • They growl if touched while sleeping.
  • They do not allow children to touch them.
  • They growl when they're groomed or when their nails are clipped.
  • They dislike being touched on the head/shoulder area.
  • They do not like to be touched from above.
  • They are aggressive when given medicine or shots.
  • They growl if their toys are touched.
  • They do not let children near their toys.
  • They get too rough when playing.
  • They react aggressively to being reprimanded.
  • They chase cars, small animals, joggers, or bikers
  • They lunge toward other dogs or people.
  • They act aggressively towards strangers.
  • They act overly protective of their owners.
  • They growl if their owner shakes hands with or hugs another person.
  • They bark aggressively at other people when in the car.
  • They act aggressively and are very territorial.

It can be very harmful to ignore these signs in the hopes that they will disappear. Unfortunately, these behaviors often return and grow in intensity if they are not nipped in the bud. If your dog displays any of these signs, please don't try to solve them on your own. Instead, consult with a veterinary behaviorist or a certified applied animal behaviorist.

Possible Causes of Aggressive Behavior in Dogs

There are many possible causes of aggressive behavior in dogs. Some of these have to do with underlying medical or physical conditions.

Painful Medical Conditions

It is very important to have a veterinarian rule out any physical conditions that might be affecting such behavior, especially if the unwanted behavior is abnormal and/or sudden. Even the most docile dogs can sometimes become quite aggressive if they are in pain. An example of this that is quite common is when a very well-tempered dog suddenly snaps when its head is touched because of an underlying painful ear condition. For more on this, read "Medical Causes for Dog Aggression."


Another issue that may cause behavioral changes is a condition called 'hypothyroidism. It is certainly worth discussing with the vet to see if your dog has this condition. All it takes to rule it out is a thyroid blood panel.


Hormones also play a role in aggressiveness. Well-behaved male dogs suddenly become aggressive when they detect a female in heat nearby. While neutering may help a male dog have a better disposition, it is not really a ''cure-all'' for major behavioral problems that are not hormone-related. For more about this read "Pros and Cons of Neutering Dogs."

For Further Reading

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2009 Adrienne Farricelli


Cherie on December 11, 2019:

Hi I have a 2 1/2 year-old Woollahra which I rescued took me five days to catch her she learnt to trust me add her to sex put it into my name the owner didn’t want her back but having issues with my husband she seems to not be able to play without getting serious couple of times he’s walked in the back gate and she’s got quite aggressive and it actually frightened me a bit that he was going to get bit just wondering what may cause this is it her pass or are they just known to be very possessive

carolyn on October 21, 2019:

I have a 9 yr old germen shepard I've had him for almost 9 yrs. i has gotten so he barks and tries to nip at my sons when they come to visit He has always loved the boys, he is in good health but the barking is really getting to all of us. Any idea why after all these yrs he is acting like this

Sam on December 13, 2018:

I have a 3 month old golden retriever. Shes been a biter since day we brought her home. We are consistent with directing her attention to toys, and still continues to try and bit us. My child will be sitting quietly and shes on them like white on rice pulling clothes growling. Recently with her bones shes turned very aggressive drawing blood from me twice. Pretty badly. Iv pet her while eating and even fed her out of my hand n shes been fine. Until now. I do basic training daily. Sit, shake, stay, down. Play fetch. For example im training her to stay off my couch, and when she doesnt like my behavior correction she becomes very aggressive.

Bryan on October 08, 2018:

The bad behavior of my dog forced me to investigate how I could train him. I found this system online and it has given me excellent results, ! He no longer bites my furniture, or my shoes, no longer urinates in the room, and no longer barks like crazy!

Jean on June 12, 2018:

We have a rescue Boston Terrier. We got him when he was 1-2 years old and have had him for 7 years . He was found on the street sick and skinny. We had a trainer come into our home when we first got him. He was aggressive toward other dogs. The trainer felt he was abused by humans and dogs. He has bitten me in the past, minor but drew blood and caused bruising. Recently as I was walking out the door with my one year old granddaughter he lunged at me and wouldn't stop biting me. I have numerous bites and huge bruises. Fortunately he didn't get my granddaughter but did attempt to. Our vet said he is beyond training. He said if his dog did that to his wife he would be put down. I'm afraid of him but love him so much. I worry he will go after my granddaughter. He doesn't bite my husband but does get angry at him. What is your advice?

Nemon on February 19, 2018:

My dog has never displayed any of these behaviors, yet she HURT another dog. She fought a dog giving NO PERCEIVABLE WARNING. None. She didn't growl, she didn't bare her teeth, she definitely did not bark. She just snapped. She went from happily sniffing butts to I'm-going-to-rip-your-throat-out in milliseconds. I don't trust her with any dog anymore, even though she's always loved meeting and playing with most dogs. It wasn't territorial, it was not about food, not about protecting me or fear or pain.

No article I've read addresses this kind of aggression or how to manage it. Now I have a mini-heart attack every time there's another dog near us while we're walking even if nothing is going on and they are twenty feet away. I don't even fully trust her with people anymore (though she's never EVER acted even remotely aggressively towards a human).

She's a five year old Staffordshire Terrier mix. Is it really a "Pit Bulls-are-evil-silent-killers" behavior? What am I to do? Dare I ask, will she turn on me? She is so subdued and tolerant and happy I never imagined she could be aggressive like she was. But she WAS. I don't trust her anymore and it feels wretched.

Adrienne Farricelli (author) on February 18, 2018:

Heidi, have a dog trainer/behavior consultant see your dog. He/she may help you with a counterconditioning/desensitization program. Good that you haven't reprimanded him as that would just add fuel to the fire.

Heidi R on February 11, 2018:

I have a two year old standard poodle who is a little on the protective side--of me and of his home and yard. He never growls, but has grabbed at people's hands and freaks out if a stranger approaches me too suddenly. If someone comes into the house, I usually distract him with a chew treat and he eventually settles down. I sense that he is insecure and nervous, so I haven't reprimanded him for this behavior in the past, fearing it might make him even more anxious. Any suggestions?

John Watson on November 11, 2017:

My brothers Labrador has just tried to bit my feet in a very aggressive loud attack. I was wearing shoes so no damage. The dog was sleepy , had just woken and showed no real warning sign. It looked at my feet and just went after them.

sarah on November 15, 2014:

Thank you

Adrienne Farricelli (author) on November 15, 2014:

Sounds like a serious case of resource guarding. I would recommend consulting with a behavior professional that can guide you through behavior modification. The below article gives an example of behavior modification for resource guarders but must be implemented with a behavior professional for safety, so please find a professional to help you out.

sarah on November 15, 2014:

Hi we are expecting a baby in 8 months time and have some concensa about are dogs behavior such as he steels food and when u try and get it back he will grown come towards u a bite u when I try and eleven my daughter up he will sit next to her and growl at me if I put my hands near he will bite he sleeps in bed with me and my boyfriend he is OK most times but if u get out of the bed and get back in he will do the same he is continually humping if he has something he should not have glands u want *t back HDTV will show bad aggression what do we do: ( other than that he is loving likes lots of cuddles says good morning to us in the morning

Adrienne Farricelli (author) on May 04, 2013:

Monu, I can write a book on the topic, I am sorry to hear you found it bland. However, if you see I have several links throughout the article if you wish to expand on the topic. Notice that this is about the "signs" so if I were to write about dog ownership, it would be off topic for this title and would turn out being too long. Please also note I am not for the assertive strategy when it comes to aggression. I treat several cases of canine aggression and don't use this approach and more than rules and boundaries I am for management. If you wish to expand on the topic note that I have many articles tackling this as I have treated many cases of dog aggression in my career.

monu on May 04, 2013:

what a bland article. iT Doesn't seem to explore why dogs seem to have these problems- most problems that occur in dogs are due to owners not being assertive enough or not setting rules and boundaries which aggression can be a typical behaviour of. How about educating people on what they can do to avoid this

Stacey on April 08, 2013:

Thank You

Adrienne Farricelli (author) on April 07, 2013:

Sorry, we're not that widespread yet! You can find good force-free trainers though by looking at the Pet Professional Guild website. Best wishes!

Stacey on April 07, 2013:

Arizona is quite a ways from South Florida... Any chance you have an affiliate/ associate here in Florida?

Adrienne Farricelli (author) on April 07, 2013:

Yes, I agree, there are quite many options when it comes to training. Maybe you can come see us at Rover's Ranch Home in Arizona, we'll work on any issues your dog has as we offer board and training! Kind regards!

Stacey on April 07, 2013:

Our Bear is a 3 year old Chocolate Lab, fixed with a few skin issues but otherwise healthy. He is an amazing watch dog, is gentle with my cats and LOVES my kids. Lately he has developed food aggression - not the kind of food aggression where you can't approach him at his dish... but rather while my kids are eating, walking with food, or carelessly talking with food in their hands. He has tried to steal food from them and inadvertently bitten them, as soon as he scarfs down his stolen food (with or without biting) he runs and hides because he knows he's done something wrong. We have tried to get our kids to be more careful around him (he will not approach the table) but it seems now he's has become a bit more brazen and has bitten my son while he was bringing scraps to the composter. He bites while in the act of stealing or eating the stolen food. This is the same dog that will let you reach into his bowl while he's eating with no issues at all, so I've found most of the food aggression behavior modification techniques to be geared towards a totally different issue. Please help, the kids are afraid I'm going to find him a new home -and if he bites them again - I'm afraid they might be right

JTJ on April 07, 2013:

No, I've never heard of a class like that - I'll have to look into it. I'm from Australia and I find besides basic training, classes are quite limited here in variation. Even finding a good behaviorist was almost impossible. We are moving to the US in July (dog and I), and I'm excited for the many classes and possibilities there in the dog world! So I'll definitely start looking out for those kinds of classes when I arrive! And checking out your hub now, thanks!

Adrienne Farricelli (author) on April 06, 2013:


For the barrier frustration, have you ever though about enrolling him to a reactive rover class? These are classes often organized by trainers and specialized in cases such as yours. For protective of the car behavior, see if my hub can help you:

JTJ on April 06, 2013:

My dog has most of the problems listed under "exposed to outdoors", I feel this is due to a mixture of a lack of proper socialization (on my part) - and several bad experiences he's had outdoors and on leash (neighbor hit him, dogs have attacked him, etc).

He's very leash reactive/aggressive. He'll be perfect and playing with another dog one minute, but as soon as that leash is on or I hold his collar, he'll get very aggressive at the other dog. Same goes for behind a door/fence/window, yet have them on the same side together and he plays perfect. I've been told this is 'barrier frustration', that comes across as very aggressive. It's really hard to take him anywhere or on walks, so sadly we don't get to do much out of the yard, as everywhere has to be on leash. I wouldn't want to take him anywhere off-leash either for a fear of just in case he does have a freak-out moment.

He also barks in the car aggressively at people outside of the car - I don't know if that one also falls under barrier frustration, or just strangers in general. Sometimes in the car he's fine, others not so much. It's odd. He also will not growl, but more of a sigh/sulky groan if I move around too much in bed and he's on the end of the bed - but this started after I accidentally pushed him off the bed in my sleep. I must have moved my leg and he slipped off, so now anytime my leg moves he panics..

I got a behaviorist to come see him, she said he's an incredibly unsure and anxious/nervous dog, but in no way is he "aggressive". Watching her work with him was incredible. She worked mostly on 'energy' etc, she took him down to a busy carpark on leash and had strangers/men walk up to her and shake her hand while he sat next to her not even looking at the stranger. It was incredible. I'm still lacking that leadership and calm/assertive that she has, but hopefully soon I'll be able to be calm/assertive and have that same control.. I find that he has a bit more confidence when he's around other dogs, so at a dog park he's great with everyone. BUT - we haven't been to a dog park in a very long time as our last trip there a man started kicking all the dogs for fighting, even the ones who were just in the area of the fight. My dog wasn't fighting, but I saw the mans foot come at him and I got down and scooped up my dog, told the man 'where to go', and left the park. Haven't been back since..

Adrienne Farricelli (author) on March 23, 2013:

Answered to your post on the hub "signs a dog is about to bite"

Lyn on March 23, 2013:

I have a one year old lab/catahoula leopard. He's a sweetheart loves people has shown no signs of aggression. We took him on a hike recently with some friends and another dog. The other dog was off the leash as ours was on a leash. They did very well together the whole hike. When walking back to the car our dog ran ahead to the other and latched on to his ear. He had a good grip on the ear wasn't making any noise or moving. He would not let go when told and wouldn't let go when he was approached and told no, drop. Eventually we had to pry is myth open. He did not puncture the other dogs ear, no blood. Should we be worried he was trying to hurt the other dog or he is secretly aggressive?

Adrienne Farricelli (author) on August 26, 2012:

Can you please provide more details, please? Does she go to the door to tell you she has to go out and becomes aggressive then? What kind of aggression do you see? Growling, trying to bark, snarling? Have you tried to ask for a sit and reward her before sending her out?

Ann on August 25, 2012:

My lab gets aggressive when she wants to go out to go to the bathroom...she doesn't bark...what would you suggest that I do?

Adrienne Farricelli (author) on June 09, 2012:

You need to take care of this problem as it is getting out of hand. A protective dog should protect only when there is a real threat. Your dog is not supposed to be taking this role which he is not temperamentally able to do withstand. I recommend seeing a professional at this point. I would also not allow this dog to follow her every where and develop this dysfunctionally strong attachment. Here is an article about protective behavior:

magicaamy on June 09, 2012:

We have a malamute and for the most part he is great. However he is overly protective of my teenage daughter. He has to be with her 24/7 and if she goes away for a night or even during school time he pouts and walks around looking for her. But what my concern is he growls when we try to wake our daughter up. He lays his body on top of her. We use to think that him being so protective of her was a good thing but, my husband and I mean no hard to our child yet the dog acts like we are trying to harm her. Even if she ismt sleeping and we go toards her he gets between her and us sometimes making a small growl and sometimes just to be inbetwen us.How can I break him of this habit and still keep him protective of her from strangers and such. TY in advance

Betty Hamnett on April 07, 2012:

The humane society tells you that the dog doesn't like other dogs, so you take the dog on walks without a lease to be able to attack other dogs, did you not understand what they said about the dog? I hope you paid for the vet bills because of you negligence.

Josue Nieves from Florida on May 03, 2011:

very informative hub,thank you for all the excellent information.

EA on March 28, 2011:

I adopted a dog from the local humane society. the humane society told me 'he doesn't like other dogs'. brought him home, when I took him for walks, I noticed he would charge other dogs visciously. I was worried about it so I called the humane society. Beforethey got back to me the dog attacked the neighbors dog, bit him in the back and had him pinned down before the neighbor could get him off the dog. Luckily the neighbor works with dogs. I sent him back to the humane society and told them to put him down. The last I heard, they will not put the dog down. The trouble is, this dog is dangerous.

Adrienne Farricelli (author) on January 02, 2011:

Tammy: your dog evidently dislikes getting its toenails trimmed.. and has learned how to stop you from doing it.. try to make nail trims pleasant again... here are some tips:

Adrienne Farricelli (author) on January 02, 2011:


Many dogs dislike being bothered when they are sleeping.. I would discourage petting when a dog is asleep.. really any dog.. you never know.. they may be having a bad dream or wake up startled and react..

Leaning over him may be seen by him as something threatening or some way of your husband establishing dominance over he feels the need to correct him with a growl...

I would recommend leadership exercises for both of you... he should not be protective of you and follow you everywhere and he should not be growling inappropriately at your hubby...(however, leave him alone when sleeping).

Stop him from following you at all times.. it may look like a form of love but it really is a form of control, sort of like a jealous wife controlling a husband's whereabouts..

You must take over and be in charge.. he thinks he rules the house and can do what he likes... with leadership exercises things may improve and he may start to relax...

here is a good article:

maria on January 01, 2011:

my german shepard is very protective of me he loves me to death never leaves my side but the problem is with my husband he growls at him when he if pated when asleep or lend over but it has been this way with a couple of our dogs i dont wana get rid of him because it will only happn again with another dog...thank you.

tammy on July 07, 2010:

I have a year old dog, he is dangerously aggressive he won't let you brush him or hell bite, you can NOT touch his toenails he will growl and bite and when I try and rub him even when he is wagging his tail and is happy he will try and bite me. When he has done something bad and I discipline him he bites me and growls and it is extremly frightening. And when he gets this look in his eyes like I see in red zone dogs on tv he has that same look and he just stares at me like its a war. I've had him so long putting him doiwn will be heartbreaking. I'm so confused, I don't think ceaser milan could fix him.

Doggie Devotee from Danville KY on March 15, 2010:

Great informations, a lot of owners seem to ignore some of the signs their dogs are giving.

Adrienne Farricelli (author) on December 13, 2009:

For the food aggression issue this hub may help you out

Food aggression is more of a trust issue. About her turning on you because she is a German Shepherd, I really think that any dog can turn on their owner if there is no discipline and dogs run the household.

Mrs.Nita on December 12, 2009:

I really appreciate this article. I have a 3 year old German Shepherd. I'll admit, she does have food aggression and we've tried to break this every since she was a puppy. I've gotten to the point where I just won't touch her when she eats and usually she eats alone. I've also noticed that when in the yard she tends to bark and everyone who comes by and if she sees another dog she'll bark and then she'll go and pick up one of her toys;growling and shaking the toy in her mouth. Her hair is standing up when she does this. When I catch her doing this, I make her come and sit down. She doesn't like to be still, so she knows she's being punished. After sitting for awhile, I allow her to get up and she's better, she may run and pace the yard but she won't show aggression. I'm not sure how to break her aggression and what's worse is that I keep hearing people say that German Shepherds will turn on you so

I think deep down inside I have that fear.

Adrienne Farricelli (author) on August 27, 2009:

My dad was once bit the same way. My dad was visiting a farm and there was this dog that looked pretty quiet. Once, he turned around he got bit pretty well. These are the ''silent biters'' that often decide to bite once the person turns their back. They usually will bite and leave because it is out of fear more than aggression.

emievil from Philippines on August 27, 2009:

I agree with a lot of points in your hub. One thing I want to add is that if you are around dogs who are not familiar with you (dogs that you have seen the first time or you seldom see) do not go near them at once. This is true whether they are barking at you or are silently looking at you. One of my dogs does not growl, he does not bark aggressively or sometimes he does not bark at all, but when a local water delivery guy crossed his path, he approached the guy and bit him, sinking two of his fangs! I panicked and got the guy to take his shots at once. That was a wake-up call for us and for the people who go inside our house.

Susan Reid from Where Left is Right, CA on August 25, 2009:

This is a good wakeup call for dog owners. I can't tell you how many times I've encountered dogs and wondered if they were friendly or vicious.

Another behavior that I find difficult to interpret is dogs barking. When you walk by their yard or their car and they are in the car. I assume they are claiming their territory and thus do not approach.

Thanks for this useful info! MM