If your dog suffers from constant itching, red paws, irritated ears or recurring skin problems, it’s natural to focus on the skin.
But scientists are increasingly looking somewhere else too: the gut.
A new study published in August 2026 has found an interesting difference between dogs with atopic dermatitis, a common allergic skin condition, and healthy dogs. The difference was found in the gut and involved an important part of the immune system called IgA.
The research adds to growing evidence that the gut, immune system and skin may be much more closely connected than we once realised.
Read the full study: Faecal IgA but not salivary IgA is associated with canine atopic dermatitis
What is canine atopic dermatitis?
Canine atopic dermatitis is a common condition that causes itchy and inflamed skin. Dogs may repeatedly scratch or lick themselves, have red or itchy paws, irritated ears, or sore skin around their face, tummy, armpits and legs.There isn't usually one simple cause. Genetics, allergies, the skin barrier and the immune system can all play a part.
Researchers are now also investigating whether what is happening inside the gut could be another part of the picture.
What did the new study find?
Researchers from the University of Edinburgh and Scotland's Rural College compared dogs with atopic dermatitis with healthy dogs.
They measured levels of something called IgA in the dogs' faeces and saliva. The researchers found that dogs with atopic dermatitis had significantly lower levels of IgA in their faeces than the healthy dogs. The median level was 0.98 g/L in dogs with atopic dermatitis compared with 1.78 g/L in healthy dogs.
Interestingly, they didn't find the same significant difference in the dogs' saliva. So why could something found in a dog's poo have anything to do with itchy skin?
What is IgA - and why is it important?
IgA is an antibody and an important part of the body's natural defence system.
It is found in places such as the gut, where the immune system is constantly coming into contact with food, bacteria and other substances entering the body.
The immune system has to perform quite a balancing act.
It needs to recognise and respond to potential threats while also learning to tolerate harmless substances and the enormous community of microorganisms that normally live in the gut.
IgA helps with this process.
That's what makes the finding of lower faecal IgA in dogs with atopic dermatitis so interesting. It suggests there may be differences in what is happening within the gut's immune environment in dogs affected by this skin condition.
What does the gut have to do with the skin?
Probably more than many of us realise. The gut contains trillions of microorganisms – bacteria and other microbes collectively known as the gut microbiome.
These microorganisms don't simply help digest food. They interact with the immune system and produce substances that can influence what happens elsewhere in the body. The immune system, in turn, helps control which bacteria are able to live and thrive within the gut.
Scientists sometimes describe the connection between the gut and skin as the gut–skin axis.
Put simply, what happens in the gut doesn't necessarily stay in the gut.
And this isn't the only recent research
Another study published in 2026 looked specifically at dogs suffering from both atopic dermatitis and adverse food reactions.
Although this was a small study involving eight affected dogs and nine healthy controls, the researchers found differences between the two groups.
The affected dogs had lower gut bacterial diversity, changes in particular bacterial groups and lower levels of several important short-chain fatty acids produced within the gut.
Short-chain fatty acids are produced when certain gut bacteria ferment dietary fibre and are increasingly being studied because of their relationship with gut and immune health.
Again, this doesn't prove that changes in gut bacteria caused the dogs' allergies. But it provides another interesting piece of evidence that the gut microbiome and immune system may be involved in canine allergic disease.
Does this mean every itchy dog has an unhealthy gut?
No – and this is important. The new IgA study found a connection between canine atopic dermatitis and lower levels of faecal IgA. It did not prove that low IgA causes atopic dermatitis.
We don't yet know whether changes in the gut contribute to the skin condition, happen because of the condition, or whether both are being influenced by other factors. The researchers themselves say that more work is needed to understand what lower faecal IgA means for dogs with allergies.
A gut microbiome test also cannot diagnose an allergy or atopic dermatitis.
Persistent itching, inflamed skin, recurring infections or other significant symptoms should always be investigated appropriately with your vet.
So why might microbiome testing be useful for an itchy dog?
At Biome4Pets, many of the dogs we test have symptoms such as itching, paw licking, recurring ear problems or suspected food sensitivities.
One of the things we have learned is that two dogs with very similar symptoms can have very different gut microbiomes. That's important.
It means there isn't necessarily one probiotic, supplement or dietary change that is right for every itchy dog. Our Dog Gut Microbiome Test looks at the bacterial community living within an individual dog's gut.
Using DNA sequencing, we can identify the bacterial populations present and look at factors such as microbial diversity, beneficial bacterial groups and areas of imbalance or overgrowth.
This gives us a much more individual picture of the dog's gut rather than simply making assumptions based on their symptoms.
Looking beyond the itch
Skin problems can be incredibly frustrating for dogs and their owners, particularly when they keep returning. There may be many factors involved, including environmental allergies, food reactions, parasites, infections, genetics and problems with the skin barrier itself.
The gut isn't a replacement for investigating those things. But research is increasingly showing us that we shouldn't necessarily think of the skin, gut and immune system as completely separate parts of the body.
The latest research showing lower faecal IgA in dogs with atopic dermatitis gives scientists another fascinating clue about that relationship.
We certainly don't have all the answers yet. But perhaps when a dog is persistently itchy, it is worth looking beyond what we can see on the outside.
Sometimes, part of the story may be happening in the gut.
Is your dog struggling with itching, recurring ear problems, paw licking or food sensitivities?
The Biome4Pets Dog Gut Microbiome Test looks at the bacterial community living inside your dog's gut.
Your dog's sample is analysed using DNA sequencing, and you'll receive a personalised report explaining what we've found, where there may be imbalances and practical recommendations for supporting their individual microbiome.
