Dog skin and coat products often add a list of extra ingredients to the main formula. We checked the canine evidence for seven that appear in our comparison: GLA from borage oil, prebiotics, astragalus, aloe, calendula, hyaluronic acid and hypochlorous acid. None has enough dog evidence to rate as supportive. Borage oil comes closest, but its dog trials combined it with fish oil. The topical ingredients — aloe, calendula, hyaluronic acid and hypochlorous acid — have been studied for wound care, which is a different question from itching or allergies.
Summary table
| Ingredient | How it’s used | Best canine evidence | Our rating |
|---|---|---|---|
| GLA / borage oil | Oral | Two placebo-controlled trials of borage + fish oil in atopic dogs; mixed results | Insufficient |
| Prebiotics (FOS, inulin, kestose) | Oral | One uncontrolled study of a probiotic + kestose in 15 atopic dogs | Insufficient |
| Astragalus | Oral | Laboratory and rodent studies only | Insufficient |
| Aloe | Topical | Small randomized wound-healing study (13 dogs, 3 cats) | Insufficient for skin disease |
| Calendula | Topical | Human and laboratory wound studies; no canine dermatitis trial | Insufficient |
| Hyaluronic acid | Topical | Pilot study of 12 open wounds in 10 dogs | Insufficient for skin disease |
| Hypochlorous acid | Topical | Randomized trial as an antiseptic in 34 dogs with bite wounds | Insufficient for skin disease |
GLA and borage oil
Borage seed oil and evening primrose oil are rich in gamma-linolenic acid (GLA), an omega-6 fatty acid that the body can convert into anti-inflammatory compounds. In dogs:
- In an 8-week, blinded, placebo-controlled study of 21 dogs with atopic dermatitis, groups receiving borage seed oil and fish oil had significantly lower redness and self-excoriation scores than at baseline.
- In a 12-week, randomized, double-blind trial of 60 atopic dogs on prednisolone, a borage-plus-fish-oil supplement reduced steroid use, but the difference from placebo was not statistically significant.
Both tested borage oil with fish oil, so the effect cannot be credited to GLA. In people with eczema, a Cochrane review of 27 studies of oral borage and evening primrose oil found no benefit over placebo. Rating: insufficient. Omega-3s are the better-supported fatty acid — see fish oil for skin and coat.
Prebiotics
Prebiotics are fibers that feed gut bacteria. The theory for skin is the “gut–skin axis”: a healthier gut microbiome may calm allergic inflammation. The only canine skin study we found gave 15 dogs with atopic dermatitis, who had been on prednisolone, a Lactobacillus paracasei probiotic plus the prebiotic kestose for 90 days, without a control group. With no placebo group and two ingredients, it cannot show a prebiotic effect. A 2025 meta-analysis also found no significant overall effect of probiotics on skin scores — see probiotics for itchy skin. Rating: insufficient.
Astragalus
Astragalus root is a traditional herbal medicine studied for immune effects. Evidence for skin inflammation comes from cell and rodent studies; we found no clinical study in dogs. Rating: insufficient.
Aloe
Aloe gel is used on the skin for soothing and wound healing. A small randomized study in 16 animals (13 dogs and 3 cats) with open wounds compared aloe juice or fresh gel with silver sulfadiazine cream and reported faster wound shrinkage with aloe. That is wound-care evidence, not evidence for allergic or itchy skin, and it is small. Aloe latex and whole-leaf products contain aloin, which can cause vomiting and diarrhea if eaten; dogs should not lick or eat aloe products not made for them. Rating: insufficient for skin disease.
Calendula
Calendula (marigold) extracts are used in creams and sprays for irritated skin and wounds. Evidence comes from human studies and laboratory work on wound healing; we found no controlled trial in dogs with dermatitis. Rating: insufficient.
Hyaluronic acid (topical)
Hyaluronic acid helps skin hold water and is used in wound gels. A pilot study applied hyaluronic acid to 12 open wounds in 10 client-owned dogs; it had no control group. Oral hyaluronic acid for joints is reviewed separately in MSM and hyaluronic acid for dogs’ joints. Rating: insufficient for skin disease.
Hypochlorous acid
Hypochlorous acid is a mild antiseptic — the same molecule white blood cells use to kill bacteria — sold as skin and wound sprays. A 2025 randomized clinical trial in 34 dogs with 51 bite wounds compared hypochlorous acid solutions with the antiseptic polyhexanide for cleaning wounds and reducing antibiotic use. It is a reasonable gentle antiseptic for minor wounds and hot spots under veterinary guidance, but antiseptics do not treat the cause of allergic itch. Rating: insufficient for skin disease.
What to do with this
If a product’s main active is one of these ingredients, the evidence is thin. If they are extras in a fish-oil product, judge the product by its EPA and DHA content. For topical sprays and gels, use them for what they were tested for — minor wounds — and see a veterinarian for itching, hot spots that spread, or skin that smells or oozes.
For a label checklist, see How to check a dog skin & coat supplement label.
Dog Supplement Facts evidence status
INSUFFICIENT for all seven ingredients as treatments for skin or coat problems, under our rating rules.
Related Dog Supplement Facts content
- Fish Oil vs Allergy-Support Chews for Dogs
- Ceramides and Fatty Acids for the Skin Barrier
- Dog Skin & Coat: What Matters
- Best-selling dog skin & coat supplements vs the evidence
In our comparison: products that list any of these seven ingredients
53 of the 285 dog skin & coat products we compared list any of these seven ingredients (19%). 2 of them are among the 20 most popular products, and their median popularity rank is #126 of 247 ranked products. Our ingredient-level evidence rating for any of these seven ingredients: insufficient.
Product-level ratings, which look at the whole formula: 49 mixed, 4 insufficient.
Most popular of these:
- #3Zesty Paws Dog Allergy Chews - Dog Allergy Relief, Lamb, 90 Ct — Mixed
- #8Zesty Paws Dog Allergy Relief Chews, Dog Probiotics for Itchy Skin and Ears, Salmon, 90ct — Mixed
- #27PetLab Co. Allergy & Immune Probiotic Chews, 30 Soft Chews, Pork — Mixed
- #35Pet Honesty Dog Allergy Chews for Itch & Allergy Relief, Salmon, 90ct — Mixed
- #36Pet Honesty Dog Allergy Chews for Allergy Relief, Peanut Butter, 90ct — Mixed
See all 53 in the comparison table →Best sellers vs the evidence
Popularity is a relative rank within our comparison (purchases, review volume and star rating), not Amazon's Best Sellers Rank and not a measure of effectiveness. Listing data collected September 2026.
Frequently asked questions
Does borage oil help dogs with itchy skin?
The dog trials tested borage oil together with fish oil. In one 8-week placebo-controlled study of 21 atopic dogs, the combination reduced redness and self-trauma scores; in a 60-dog trial it lowered steroid use, but not significantly. A human Cochrane review of borage and evening primrose oil for eczema found no convincing benefit.
Is aloe vera safe for dogs?
Topical aloe gel is generally considered safe on intact skin. The whole leaf and latex contain compounds (aloin) that can cause vomiting and diarrhea if eaten, so dogs should not lick or eat aloe products not made for them.
Does hypochlorous acid spray help dogs' skin?
Hypochlorous acid is an antiseptic. A randomized trial in dog bite wounds tested it for wound cleaning. That supports its use as a gentle antiseptic, not as a treatment for allergic itch.
Do prebiotics help dogs with skin allergies?
It has not been shown. The canine skin study we found gave 15 atopic dogs a probiotic plus the prebiotic kestose without a control group, so the prebiotic's effect cannot be separated.
What skin supplement ingredient has the best evidence for dogs?
Omega-3 fatty acids (EPA and DHA from fish oil), mainly as an add-on for allergic skin and for coat quality — although even that evidence is mixed.
References
- A blinded, placebo-controlled study of the efficacy of borage seed oil and fish oil in the management of canine atopy. 1999. PMID: 10331227. https://pubmed.ncbi.nlm.nih.gov/10331227/
- Saevik BK, et al. A randomized, controlled study to evaluate the steroid sparing effect of essential fatty acid supplementation in the treatment of canine atopic dermatitis. Vet Dermatol. 2004;15(3):137–145. PMID: 15214949. doi:10.1111/j.1365-3164.2004.00378.x
- Bamford JT, et al. Oral evening primrose oil and borage oil for eczema. Cochrane Database Syst Rev. 2013. PMID: 23633319. https://pubmed.ncbi.nlm.nih.gov/23633319/
- Clinical effects of combined Lactobacillus paracasei and kestose on canine atopic dermatitis. Pol J Vet Sci. 2023. PMID: 36961289. https://pubmed.ncbi.nlm.nih.gov/36961289/
- Aloe barbadensis Miller versus silver sulfadiazine creams for wound healing by secondary intention in dogs and cats: a randomized controlled study. Res Vet Sci. 2018. PMID: 29131970. https://pubmed.ncbi.nlm.nih.gov/29131970/
- Application of hyaluronic acid in the healing of non-experimental open wounds: a pilot study on 12 wounds in 10 client-owned dogs. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4774664/
- Dog-to-dog bite wound management — comparison of the antiseptic efficacy of polyhexanide and hypochlorous acid with regard to reducing the use of antibiotics: a randomized clinical trial. Vet J. 2025. https://www.sciencedirect.com/science/article/pii/S1090023325002096
- Pacheco RCF, et al. Probiotics as an adjunct in the treatment of canine atopic dermatitis: a systematic review and meta-analysis of in vivo studies in dogs. J Vet Med Sci. 2025;87(9):1068–1077. doi:10.1292/jvms.24-0471