Quercetin for Dogs With Allergies: What the Evidence Shows

Quercetin is a plant flavonoid found in apples, onions, capers and many other foods, and it is sold in dog supplements as a natural antihistamine — often called “nature’s Benadryl”. We found no controlled trial of quercetin for allergies or itching in dogs. The antihistamine-like effects come from laboratory studies, and a canine absorption study found that only about 4% of an oral dose of quercetin reaches the bloodstream.

Key takeaways

• No placebo-controlled trial has tested quercetin for itching or allergic skin disease in dogs.
• In nine beagles, the absolute oral bioavailability of quercetin was about 4%.
• The “antihistamine” claim rests on cell and rodent studies of mast cells.
• A positive diet trial in allergic dogs tested a food fortified with omega-3s, antioxidants and polyphenols together, so it cannot show what quercetin did.
• Omega-3 fatty acids have more evidence as an add-on for allergic skin, and prescription treatments work much better than any supplement.

Why quercetin is marketed for allergies

Allergic itch in dogs involves mast cells, immune cells in the skin that release histamine and other inflammatory signals. In laboratory studies, quercetin reduces mast-cell release of these mediators and has antioxidant effects. Small human studies have reported benefits in allergic conditions. From this comes the “natural antihistamine” label.

Two problems separate that mechanism from a result in dogs. First, lab concentrations are often far higher than what reaches tissues after an oral dose. Second, histamine is only part of canine atopic dermatitis: even prescription antihistamines have limited effect on it, which is why international guidelines give them a small role.

What the canine evidence shows

Absorption: low

A 2010 study gave nine adult beagles quercetin and related compounds at 10 mg/kg by mouth. The absolute bioavailability of quercetin was about 4%, more than 80% of what circulated in the blood was in the form of conjugated metabolites rather than free quercetin, and a large share of the absorbed amount was removed through bile. Isoquercitrin (a quercetin glucoside) was absorbed about one and a half times better than plain quercetin. Most dog supplements do not say which form they use.

Clinical trials for allergy: none for quercetin alone

We found no randomized or controlled trial of quercetin on its own for itching, atopic dermatitis or other allergic disease in dogs.

The closest study is a 2021 randomized, double-blind, placebo-controlled trial in 40 dogs with atopic dermatitis that compared a therapeutic diet fortified with omega-3 fatty acids, antioxidants and polyphenols (the group of plant compounds that includes quercetin) with a control diet for 60 days. Lesion scores fell 49% from baseline by day 60 and owner-rated itch fell 46% on the fortified diet, while the control diet did not change significantly. It is encouraging for the diet, but with several actives — including omega-3s, which have their own evidence — it cannot be credited to quercetin.

Other canine studies of quercetin concern unrelated outcomes, such as a 2025 metabolomics study of a quercetin-enriched prescription diet, and tell us nothing about itch.

Safety

Quercetin is used in dog foods and supplements without reported problems at typical amounts. Long-term safety at supplement doses has not been studied in dogs. Quercetin can affect liver enzymes that metabolize some drugs, so check with your veterinarian if your dog takes regular medication or has kidney or liver disease. Onion is a food source of quercetin but is toxic to dogs; never use onion as a “natural” source.

How to read a quercetin product label

• Is the amount per chew stated in mg? “Allergy blends” often list quercetin without an amount.
• Which form? Quercetin dihydrate, isoquercitrin and rutin are absorbed differently.
• What else is in it? Many allergy chews combine quercetin with fish oil, probiotics or colostrum. Any effect may come from those — see fish oil vs allergy-support chews and probiotics for itchy skin.

For a full checklist, see How to check a dog skin & coat supplement label.

Dog Supplement Facts evidence status

INSUFFICIENT

There are no controlled canine trials of quercetin for allergies or itching, absorption in dogs is low, and the one positive diet trial tested several actives together. Under our rating rules, quercetin is rated insufficient.

When to see a veterinarian

Itching that lasts more than a week or two, recurring ear infections, licking the paws, hair loss, red or crusty skin, or a smell from the skin are signs that need a diagnosis. Fleas, food allergy, environmental allergy and infections each have specific, effective treatments.

Related Dog Supplement Facts content

• Fish Oil for Dogs’ Skin and Coat
• Vitamin E for Dogs’ Skin
• Apple Cider Vinegar for Dogs’ Itchy Skin
• Best-selling dog skin & coat supplements vs the evidence

References

1. Reinboth M, et al. Oral bioavailability of quercetin from different quercetin glycosides in dogs. Br J Nutr. 2010. PMID: 20230651. https://pubmed.ncbi.nlm.nih.gov/20230651/
2. de Santiago, et al. Randomized, double-blind, placebo-controlled clinical trial measuring the effect of a dietetic food on dermatologic scoring and pruritus in dogs with atopic dermatitis. BMC Vet Res. 2021. doi:10.1186/s12917-021-03063-w
3. Exploring the effects of quercetin-added pancreatic diet on metabolic homeostasis in dogs via metabolomics. PLoS One. 2025. PMID: 39946409. https://pubmed.ncbi.nlm.nih.gov/39946409/
4. Beynen AC. Quercetin for dogs. 2020. https://www.researchgate.net/publication/340998452_Beynen_AC_2020_Quercetin_for_dogs
5. Olivry T, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Vet Res. 2015;11:210. doi:10.1186/s12917-015-0514-6