Have a friend your dog hates? They dislike people for a reason most wouldn't consider.

Tod Perry
Sun, 19 Oct 2025 18:57:47 +0000
Angry dogs, Animal researcher, Barking dog, Calm dogs, Canine reactions, Dog hates friend, Dog training, Dog treats, Dogs, Dogs and people, Dogs enemies, Olfactory bulb, Pets, Scared dog, Scents, Upset dogs, Violent dogs

Does your dog freak out when one of your friends comes by the house, and you don’t know why? Do they bark, growl, or worse, nip at their ankles when they come to the door? Strangely, some dogs have a real problem with people who were always nice to them.

But according to science, there’s a good reason for it. Dogs have an incredible sense of smell, closely linked to memory, and that's where the trouble begins.

Let’s start with the most important part: your dog’s incredible ability to smell means they perceive the world in a way that you could never imagine. Humans have around six million smell receptors, but dogs can have up to 300 million. Dogs also have a massive olfactory bulb that occupies around 10% of their brain. A dog's ability to smell is 10,000 to 100,000 times greater than that of a human, so they are perceiving the world in a way we could never fathom.

Why do dogs dislike certain people?

Now, let’s say your friend Frank stops by the house and your dog gets stressed. The hair stands up on its back, its tail is alert, and it begins to bark like crazy. Why does he have such a problem with Frank? According to researchers, it's because he smells like a memory associated with danger.

For example, an animal researcher reported in the book The Other End of the Leash that their dog bit certain people who came to their house. They discovered that each of them had eaten pizza before they came over, and that a pizza delivery guy had once kicked the dog. The dog associated the smell of pizza with danger. Therefore, if someone came by smelling like pizza, you could be sure they were in trouble.

So, your friend Frank could be wearing cologne, using laundry detergent, or drinking the same type of tea as someone who was mean to the dog in the past, and your poor fur baby is taking it out on your buddy.

Angry dog. via Canva/Photos

If Frank came to your house one day smelling like something he shouldn’t, then your dog could mark them for life as a threat until they are trained to think otherwise.

It’s not just food and perfumes that dogs pick up on. Dogs can also smell human emotions and tell whether people are calm, fearful, or on alert.

Here are some other signs that your dog picks up on when your friends come over, shared by Futura:

1. High stress or anxiety levels

2. Unusual chemical smells

3. Body language and tone of voice

4. A person’s resemblance (scent, posture, behavior) to someone from the dog’s past

5. Undetected health issues

A dog getting a treat. via Canva/Photos

How to make your dog like someone

It’s not totally shocking that one way to reverse your dog's negative opinion of your friend Frank is that next time he comes over, he should approach your dog slowly, with a relaxed posture, and then offer them a high-value treat. Not a run-of-the-mill dog bone but something your dog really likes.

“Through desensitization and counterconditioning, you’ll be able to help your dog make positive associations to the presence of people and slowly shift your dog’s feelings and behavior around meeting new people,” the American Kennel Club's Sassafras Patterdale writes.

If you’ve always wondered why your dog had big reactions to safe people, now you know that it’s because they are keyed into a part of reality that you can’t perceive. It doesn’t make the dog bad, and it doesn’t mean Frank has something to hide. It just means that you and the dog experience the world (and Frank!) in very different ways.