Understanding the gut, immune system, and stress cycle in allergic dogs
When dogs begin scratching in spring, we tend to focus on what’s happening on the skin. However, emerging research suggests the processes behind persistent itching may be more complex.
Certified Natural Animal Nutritionist Rachael Tricarico explores the connections between the gut, immune system, skin and behaviour — and why breaking the itch–lick–stress cycle may require looking beyond the itch itself.
Spring arrives and, for many dog owners, so does a familiar sound: scratch, lick, chew, repeat.
Perhaps your dog suddenly starts licking their paws every evening. They rub themselves along the grass, scratch during the night or begin chewing persistently at the same patch of skin. So what is making them so itchy?
|
| Licking paws constantly? It's often the first sign of environmental allergies or irritated skin. |
The answer isn’t always straightforward.
Itching can have many causes, including parasites, environmental allergies, food reactions, contact irritation, dry or damaged skin, and secondary bacterial or yeast infections. Persistent or recurrent itching should therefore be investigated by a veterinarian rather than assuming allergies are responsible.
For dogs prone to allergic skin disease, spring can be particularly challenging. Pollens, grasses and other environmental allergens become more prevalent, while warmer weather can mean dogs spend more time outdoors and have greater contact with potential triggers.
We naturally look at the skin when a dog starts scratching. Yet the skin does not function in isolation so we need to look at a more holistic level.
Researchers are increasingly investigating the relationships between the gut microbiome, immune system and skin. Add another important piece — the brain and behaviour — and an interesting picture begins to emerge.
An environmental trigger may cause a dog to itch. The dog licks or scratches for relief. Repeated licking further irritates an already uncomfortable area. The skin barrier can become compromised, potentially creating even more discomfort. The dog becomes restless and continues licking.
What began as an itch can become an itch–lick–stress cycle that is increasingly difficult to interrupt.
This doesn’t mean anxiety causes allergies, or that every itchy dog has an unhealthy gut.
It does suggest that when we’re trying to understand the chronically itchy dog, we may need to look beyond the surface.
This is where the emerging science of the gut–brain–skin connection becomes really interesting.
What Is the Gut–Brain–Skin Axis?
The gut, brain and skin might seem like three completely separate parts of your dog’s body, but they are constantly communicating through the immune system, nervous system and chemical signals produced within the body.
At the centre of much of the emerging research is the gut microbiome — the vast community of microorganisms living in your dog’s digestive tract. These microorganisms don't simply help with digestion. They interact with the immune system and produce compounds that can influence processes elsewhere in the body.
This interaction is particularly relevant because the gut is an important site of immune activity. The intestinal barrier, gut microorganisms and immune system are in constant communication, helping the body respond appropriately to what it encounters.
Researchers are now investigating how changes within this environment may influence immune responses beyond the gut, including those involved in inflammatory skin conditions. This is one of the key ideas behind the gut–skin axis: what happens in the digestive tract may have effects that extend well beyond digestion.
That matters when we talk about itchy skin because many of the conditions behind persistent itching involve the immune system.
In dogs with environmental allergies, the immune system can overreact to otherwise harmless substances such as pollens, grasses or dust mites. The resulting inflammatory response contributes to the redness, irritation and itching owners see on the skin.
Researchers have found differences in the gut microbiome of dogs with canine atopic dermatitis compared with healthy dogs, although we are still learning whether these differences contribute to the disease, result from it, or are influenced by other factors such as diet and medication.
This is an important distinction. Science doesn't tell us that an unhealthy gut causes allergies, or that changing the microbiome will cure an itchy dog. What it does suggest is that the gut and skin shouldn't necessarily be viewed as completely independent systems.
Now Add the Brain
Itch isn't simply something happening on the surface of the skin. It is a sensation communicated through the nervous system and interpreted by the brain, prompting a dog to respond — usually by scratching, chewing or licking.
When that itch becomes persistent, the relationship between physical sensation and behaviour can become more complex. Stress may add another layer.
This doesn't mean anxiety causes a dog's allergy, and persistent paw licking should never automatically be dismissed as behavioural.
The itch may have started with a very real physical trigger.
However, once itching becomes chronic, the factors keeping the behaviour going may become more complex. Scratching or licking can provide temporary relief from an uncomfortable sensation, making it a behaviour the dog repeats. If the licking further irritates the skin, the dog has another reason to return to the same area.
Ongoing discomfort can also affect a dog's ability to settle and sleep, potentially contributing to restlessness and stress. In this way, stress doesn't necessarily start the itch, but in some dogs it may become one of the factors that helps perpetuate the itch–lick cycle.
This distinction between what triggers the itch and what keeps the cycle going is important.
Spring provides a perfect example of how these systems can converge. A dog susceptible to seasonal allergies encounters increased environmental allergens. Their skin becomes itchy, they begin licking their paws, the skin barrier becomes increasingly irritated and the licking continues. At the same time, ongoing discomfort may affect their ability to settle or sleep.
The result isn't simply an itchy patch of skin. It is a dog experiencing a series of connected physical and behavioural responses.
Understanding those connections changes the question from “What can I put on my dog's itchy skin?” to “What is driving the itch, and what might be keeping the cycle going?”
Supporting the Gut-Skin Axis Through Nutrition
As a nutritionist, this is where I believe it is particularly important to separate promising science from promises.
Nutrition provides the building blocks required to maintain normal skin, coat and physiological function. Essential fatty acids, adequate protein, vitamins and minerals all have roles in supporting normal skin and skin-barrier function.
|
| Essential fatty acids, fresh protein, and targeted nutrients support normal skin barrier function from the inside. |
Diet is one of several factors that can influence the composition and activity of the gut microbiome. This has led to growing scientific interest in whether supporting the microbiome could, in turn, influence immune and skin health.
Probiotics are one area being investigated, alongside prebiotics, postbiotics and dietary approaches that support the intestinal environment. Research has specifically explored the gut microbiome in dogs with atopic dermatitis and whether microbiome-targeted interventions could have a role alongside conventional management.
The findings are interesting, but this is still an emerging field. Probiotics should not be viewed as a cure for allergies or a replacement for veterinary treatment.
Another consideration is that probiotics are not interchangeable. Different bacterial strains can have different characteristics, so evidence relating to one strain or combination of strains cannot automatically be applied to every product labelled “probiotic”.
For me, the more useful question is not, “Which supplement will stop my dog itching?”
It is, “What does this dog need to support their overall health while we identify and manage the underlying cause of the itch?”
That may include appropriate nutrition, supporting digestive and microbiome health, ensuring the diet provides nutrients important for normal skin function and considering sources of essential fatty acids.
These strategies form part of the bigger picture. They don't replace diagnosis and appropriate treatment.
Breaking the Itch–Lick–Stress Cycle
|
| When itching becomes chronic, physical discomfort and repetitive behaviour can reinforce one another. |
If your dog is itchy this spring, managing the problem may mean looking at several parts of the cycle rather than focusing solely on the visible patch of skin.
✔️ Investigate what's driving the itch.
Persistent, severe or recurrent itching needs veterinary investigation. Look for patterns too: when does the licking occur, where on the body, and does it coincide with particular seasons, environments or activities?
✔️ Reduce the itch burden.
Where possible, reducing exposure to known environmental triggers and supporting the skin barrier can help address some of the factors feeding the physical itch cycle. Your veterinarian can advise what is appropriate for your individual dog.
✔️ Support from the inside.
Appropriate nutrition, digestive health and nutrients required for normal skin function can form part of a whole-dog approach. Emerging gut–skin research also gives us another reason to consider the microbiome as part of this broader picture.
✔️ Consider what may be perpetuating the behaviour.
If a dog has been itchy for some time, don't overlook sleep, stress, enrichment and opportunities to settle. Where repetitive licking continues despite the underlying medical condition being appropriately managed, behavioural factors may also warrant investigation.
The aim isn't to decide whether an itchy dog has a skin, gut or behavioural problem. It is to recognise that, in some dogs, these factors may overlap.
Looking at Whole-Dog Health
Perhaps the most interesting thing about the gut–brain–skin axis isn't that it gives us another treatment for itchy dogs.
It changes the way we think about them.
The gut communicates with the immune system. The immune system plays an important role in allergic disease. The skin sends sensory information to the brain. Discomfort influences behaviour. Behaviour such as persistent scratching and licking can, in turn, affect the skin.
These systems don't exist independently or in isolation.
The science of the gut–brain–skin connection in dogs is still developing, but it is already encouraging us to ask better questions about the chronically itchy dog.
When a dog is persistently itchy, instead of looking only for something to put on the itch, we can consider what might be driving it, what might be perpetuating it and what the dog needs as a whole.
So, if the soundtrack to spring in your house has become scratch, lick, chew, repeat, don't simply ask how you can stop the scratching.
Ask what's driving the itch and what might be keeping the cycle going.
About the Author
Rachael Tricarico with her dog Lenny
Rachael Tricarico, BBus (International Trade), Certified Natural Animal Nutritionist (CIVT), is the Founder of Australian pet health and grooming brand Houndztooth, with a particular interest in evidence-led nutrition and supporting the long-term health and wellbeing of dogs. Connect with Houndztooth on
This article is provided for general educational purposes only and is not intended to diagnose or treat any condition or replace veterinary advice. Persistent, severe or recurrent itching, skin changes or excessive licking should be assessed by a veterinarian.
Sources:
Harvey, N.D., Craigon, P.J., Shaw, S.C., Blott, S.C. & England, G.C.W. (2019). Behavioural Differences in Dogs with Atopic Dermatitis Suggest Stress Could Be a Significant Problem Associated with Chronic Pruritus. Animals, 9(10), 813.
https://doi.org/10.3390/ani9100813
Thomsen, M., Künstner, A., Wohlers, I., et al. (2023). A comprehensive analysis of gut and skin microbiota in canine atopic dermatitis in Shiba Inu dogs. Microbiome, 11, 232.
https://doi.org/10.1186/s40168-023-01671-2
Rostaher, A., Morsy, Y., Favrot, C., et al. (2022). Comparison of the Gut Microbiome between Atopic and Healthy Dogs—Preliminary Data. Animals, 12(18), 2377.
https://doi.org/10.3390/ani12182377
Song, H., Mun, S-H., Han, D-W., et al. (2025). Probiotics ameliorate atopic dermatitis by modulating the dysbiosis of the gut microbiota in dogs. BMC Microbiology, 25, 228.
https://doi.org/10.1186/s12866-025-03924-6
Pacheco, R.C.F., Lins, L.F., de Brito, L.P., et al. (2025). Probiotics as an adjunct in the treatment of canine atopic dermatitis: a systematic review and meta-analysis of in vivo studies in dogs. Journal of Veterinary Medical Science, 87(9), 1068–1077.
https://doi.org/10.1292/jvms.24-0471
Miller, J., Simpson, A., Bloom, P., et al. (2023). 2023 AAHA Management of Allergic Skin Diseases in Dogs and Cats Guidelines. Journal of the American Animal Hospital Association, 59(6), 255–284.
https://doi.org/10.5326/JAAHA-MS-7396
