For the first time, there is a postbiotic — Pediococcus acidilactici — with peer-reviewed clinical proof that it reduces itching in dogs. It is the first in the world. And the surprise is that its benefits don't stop at itching: a brand-new 2025 study shows it also reshapes the gut microbiome and improves stool quality.

In this article we explain — in plain language — what IL-31 is, why it is the single most important itch signal in dogs, why supplements have been powerless against it until now, and exactly how this new postbiotic works.

1. The "itch that doesn't quit" has a name — and it's a single molecule called IL-31

If your dog scratches, licks paws, chews their belly and wakes up at 3 a.m. to scratch again, there is a very good chance one tiny protein is doing most of the damage. It is called IL-31.

IL-31 is a cytokine — a messenger your dog's immune system releases. Scientists call it the "master itch signal" because 57% of dogs with confirmed atopic dermatitis have detectable IL-31 in their blood, and when researchers inject IL-31 into healthy dogs, it reproduces the entire atopic-dermatitis itch picture by itself. It is that central.

IL-31 is also why antihistamines almost never work for chronic dog itching. Histamine itch peaks within minutes. IL-31 itch peaks 2.5 to 5 hours after the trigger — it is a deep, slow, compulsive itch that ignores antihistamines completely.

2. IL-31 is the signal behind atopic dermatitis — the most common chronic skin disease in dogs

Atopic dermatitis is the #1 chronic skin disease in dogs in Europe. It is essentially an over-reactive immune system that — in response to pollen, dust mites, foods, or just an unbalanced gut — produces too much IL-31. This single molecule then:

• Fires sensory nerves in the skin → relentless scratching.
• Weakens the skin barrier → dry, flaky, infection-prone skin.
• Drives nerve sprouting in the skin → even normal stimuli become itchy.
• Disrupts oil glands → poor coat quality, yeast overgrowth.
• Wakes your dog up at night for hours.

The hard truth: until now, no supplement ingredient on the European market had any direct way to reduce IL-31. That is why even good-quality omega-3 or probiotic supplements often felt like they were "helping a little, but not enough" in atopic dogs.

For decades, IL-31 has been the wall that supplements could not get past. Owners had two choices: live with chronic itching, or move to prescription veterinary drugs. There was no middle ground.

3. The drugs vets reach for: Apoquel and Cytopoint — and what they don't do

When an itch is bad enough, vets prescribe one of two drugs that target IL-31 directly:

• Apoquel (oclacitinib) — a daily tablet that blocks the signal IL-31 uses inside the cell. It works fast but it is a drug, with side-effects to monitor.
• Cytopoint (lokivetmab) — a monthly injection of an antibody that physically grabs IL-31 in the bloodstream before it can reach the nerve.

Both work. Both are important tools. But neither of them addresses why the dog is producing so much IL-31 in the first place. They quiet the signal at the wire; they don't repair the alarm system. That is why so many dogs feel better on Apoquel — but flare again the moment the dose drops, the gut becomes unbalanced, or allergen season hits.

This is the gap supplements have been trying to fill — and where, for the first time, a postbiotic has real clinical evidence behind it.

4. Enter Pediococcus acidilactici — the first postbiotic in the world with clinical proof on dog itching

Let's translate the science. A postbiotic is what is left over after a beneficial bacterium has finished doing its work — the molecules it produced, with the bacterium itself heat-inactivated. Think of it as the "active output" of a probiotic, in concentrated form, ready to act from day one.

The postbiotic at the heart of this story is made from a strain called Pediococcus acidilactici. What makes it different from every other postbiotic is that it is indole-rich — meaning it carries a specific family of molecules that engage a powerful immune switch in the body called the AhR receptor.

And here is the breakthrough: this is the same receptor as a new FDA-approved human dermatology drug called tapinarof, which has been shown in clinical trials to reduce itching and skin inflammation in atopic patients within 1–2 weeks.

5. How Pediococcus acidilactici actually works on IL-31 — five gentle "brakes"

How does Pediococcus acidilactici actually reach IL-31? Through five gentle "brakes" on the system that produces it. Here is the picture without the jargon:

Brake 1 — It calms the "fire alarms" in the skin. When the skin meets an allergen, it normally sends out alarm signals that wake up the whole immune response. The postbiotic softens those alarms before the cascade even starts.

Brake 2 — It calms the immune cells that release IL-31. A specific group of immune cells is responsible for making IL-31. The postbiotic teaches the system to switch fewer cells into this aggressive mode.

Brake 3 — It reduces how much IL-31 is produced. The same AhR pathway is used by a new human dermatology drug, where it has been shown to directly lower IL-31 levels in the skin. The postbiotic engages the same pathway in dogs — through food, not a drug.

Brake 4 — It reduces the "docking points" for IL-31 on skin cells. Even if some IL-31 is still made, the postbiotic lowers the number of receptors it can attach to. The skin literally becomes less reactive to the same molecule.

Brake 5 — It calms the helpers that keep the itch cycle going. In laboratory tests, the postbiotic cut two key inflammation amplifiers by 100% and 35%. These are the "logs on the fire" that keep itching burning long after the trigger is gone.

In one phrase from the science team: "It does not mute the soloist — it quiets the entire symphony around it." That is exactly the upstream lever supplements have been missing.

This is what makes Pediococcus acidilactici different from any other supplement ingredient that came before it. It does not chase the itch after it has started — it turns down the volume of the immune environment that produces the itch in the first place.

6. The 2025 study that put this postbiotic on the map — Sordillo et al., 2025

The headline study is from the journal Animals (Sordillo et al., 2025). It was randomised, double-blind, placebo-controlled — the gold standard for clinical research — with 30 dogs over 28 days.

To put that 27% reduction in context: it is over 2.5× larger than any other postbiotic in published canine itch research. This is the result that earned Pediococcus acidilactici the title "the first postbiotic with proven anti-itch action in dogs."

7. The brand-new study (2025) — Pediococcus acidilactici also improves gut function

Just published in the journal Pets (MDPI) is the follow-up study, again double-blind and placebo-controlled, this time in 20 dogs with chronically loose stools but no diagnosed digestive disease.

This second study is what turns this postbiotic into a true gut–skin axis ingredient: the same molecule that helps reduce itching in atopic dogs also rebuilds digestive function in dogs with loose stools, and remodels the microbiome at the same time.

8. Why this matters: the gut–skin axis is real, and now we have an ingredient that proves it

For years, dog owners have heard the phrase "the gut is the root of skin problems." Until now, that connection was more theory than proof. With these two studies together, we finally have one ingredient with peer-reviewed clinical evidence on both sides of the axis:

For a dog owner who has tried "everything else" — fish oil, single-strain probiotics, hypoallergenic shampoos, food trials — this is the first ingredient that does not just say it works on the gut–skin axis. It has the peer-reviewed numbers to back it up, on both sides.

9. How gutQR Anti-Itch puts this postbiotic to work — alongside everything else

Pediococcus acidilactici is a key new ingredient in gutQR Anti-Itch — but it is not the only one, and it is not the centre of the formula. We designed gutQR Anti-Itch as a multi-layer system, where the postbiotic works alongside several other evidence-backed ingredients to support every relevant layer of the itch picture at once.

Here is what is inside one daily scoop:

gutQR Anti-Itch is the only product on the European market that combines the gut–skin axis, immune support, faster itch comfort and direct skin and coat repair in one formulation — and the first in the EU to include the Pediococcus acidilactici postbiotic alongside this complete stack.