Does your dog have itchy skin? Many dogs develop chronic dermatitis skin conditions (like atopic dermatitis) associated with inflammation that are often itchy and painful and may reflect an underlying dog allergy. Skin barrier weakness is often associated with these conditions, which makes your dog’s skin more vulnerable to behaviors like scratching and chewing. As a result these dog skin conditions are difficult to treat and unfortunately can end up in cycles of relapse.

‍In this article we’ll explore possible root causes of persistent itchy and painful skin experienced by many dogs, and potential treatments to target a possible culprit — the gut microbiome.  

3D illustration of bacteria in the gut microbiome

The gut microbiome is a diverse community of bacteria and other microbes that help break down food into tiny pieces (molecules) that pass through the cells of the gut to feed the body. Some of these food molecules also act as messengers that send signals — such as feeling full or feeling anxious — to different systems in the body. Members of this microbiome community also influence your dog’s immune system. In fact, it’s estimated that at least 70% of the immune system resides in your dog’s gut microbiome.

‍The skin microbiome is also a diverse community of bacteria that inhabit the skin, and this helps to keep potentially harmful bacteria from growing there.

Close up picture of dog atopic dermatitis

For dogs, allergens can initially trigger an acute allergic reaction resulting in itchy and sensitive skin, e.g., dogs with a flea allergy. When diagnosing canine allergic dermatitis conditions, many veterinarians will use a tiered approach to explore potential triggers. If the problem is more generalized, blood tests can be done to test for environmental and dog food allergies.  

‍There are several treatments for dermatitis in dogs, including antibiotics and steroids, for the itch, the ooze and the skin damage. But often these treatments result in only temporary relief, which can be frustrating for your pup and dog parents. The key is to get to the root cause and adjust your dog’s immune response.  

The gut is the largest and most complex part of the immune system of mammals. It contains diverse immune cells, bacteria and other microbes. Immune cells are the safety patrol of the body, and they monitor the gut community for danger (pathogens and toxins). When a threat is detected, the immune system mobilizes an inflammatory response to neutralize it.

In young dogs, the gut microbiome trains the developing immune system to recognize friend from foe. The gut immune system needs to learn to distinguish potential bad bacteria, which can invade and make your dog sick, from good bacteria that help to maintain the health and happiness of your canine. These helpful bacteria also modulate immune responses to avoid inflammation in your dog when it’s not needed.  

What if itchy dog flares were not caused by a single allergen, but were triggered by inflammation signals made by bacteria in your dog’s gut microbiome?

There is growing evidence that what’s happening on the skin surface may actually reflect a bacterial imbalance in the gut microbiome that is associated with inflammation. Inflammation provides an important defense against pathogens, and it’s important during the healing process. But too much inflammation can cause irritation and damage to your dog’s body. A recent study found that healthy dogs have a higher diversity — more different kinds — of microbiota than allergic dogs, including dogs with atopic dermatitis. 

‍These diverse beneficial bacteria train the immune system to respond properly to a pathogen, and avoid attacking the gut cells with an inflammatory response. Inflammation in the gut often leads to inflammation in your dog’s body, which can be a sign of a hyperactive immune system. This may be a source of skin conditions like dog atopic dermatitis (AD), which is the second most common inflammation of the skin, especially when a specific allergen is difficult to identify. Inflammation is the dog’s immune system reacting as if it has been attacked by a harmful invader.

‍If the bacterial community is out of balance, and there are more pro-inflammatory bacteria than needed, they may send signals that cause an increase in general inflammation of the body. This may explain why, in some cases of dog dermatitis, the part of the immune system that responds to an allergen is not found where it would be expected. This finding shows that the itchy dog skin is caused by a different source of inflammation other than an allergen.

‍For example, members of the bacteria Lactobacillus, are anti-inflammatory. These bacteria send signals to help calm down immune responses so the body doesn’t think it is under attack. If these organisms are reduced and not able to do their job, inflammation in both the gut and the body can increase. These immune ‘freak outs’ can lead to skin conditions like dermatitis in dogs.

‍In fact, recent studies of dogs with inflammatory bowel disease (IBD) and other chronic gut problems also show skin irritations including atopic dermatitis. IBD in dogs is also linked to changes in the healthy microbiome that has shifted to a less diverse bacterial community with certain bacteria associated with inflammation. This problem of microbiome disruption that leads to disease is called ‘dysbiosis in dogs’, which means a disruption in the harmony of the microbiome relationship with the host gut.  

The skin microbiome also plays a crucial role in flares of dermatitis, and the healing. Allergic diseases, such as atopic dermatitis, have been increasing in incidence among people and pets. Important lessons have been learned by identifying bacteria that appear during flares of irritation, and which types seem to help prevent them.

A diverse community of bacteria is critical for defense against pathogens by taking up space in the skin microbiome and making chemicals that inhibit them. When diversity decreases, spaces are left open for pathogenic bacteria that may cause inflammation, and skin barrier weakness.

‍For example, coagulase-positive Staphylococcus – a known pathogen for people and dogs – is associated with both atopic dermatitis in dogs and in people. Notably 30-100% of atopic dermatitis patients carry this Staphylococcuspathogen. That’s 1.5 -5 X higher than the normal 20% incidence of Staph in the population of healthy people. When diversity decreases, spaces are left open for Staph to grow.

There are many bacteria on the skin that make chemicals to prevent Staph from growing including Corynebacteria and and Cutibacteria. If diversity decreases, the numbers of Staph can increase, toxins cause the skin to become irritated, and weakened. The same bacteria that inhibit Staph also make beneficial substances that help the skin to recover by reducing inflammation.

The answer to this question is complex, and more studies are needed. Using dog antibiotic treatments can change the bacterial community in the gut, as do changes in your dog’s diet. After antibiotic treatment, it is especially important to help support a healthy balance in the gut microbiome.

‍AnimalBiome offers a simple, at-home microbiome Gut Health Test to find out if the bacteria your dog’s gut are out of balance. Testing a dog’s gut microbiome provides unique insight into their gut health and includes personalized dietary, lifestyle, and supplement recommendations to improve your dog’s health. Imbalances in specific gut bacteria can be addressed to help alleviate your dog’s symptoms (like itchy, red, inflamed skin) associated with a number of chronic health conditions, including dog allergies and dog skin conditions like atopic dermatitis.

‍Your dog’s diet can also have a big influence on the balance of beneficial bacteria in the microbiome. The food that you feed your dog influences which types of bacteria inhabit the digestive tract. Through diet changes, and balancing the gut bacterial community, inflammation can be controlled and may lead to long term healing. Learn more about our Gut Restore Supplements.

This article was originally published on July 28, 2019, and updated on March 4, 2022.