DMSO (dimethyl sulfoxide) is applied topically to horses as a liquid, gel, or ointment to reduce swelling and inflammation, most commonly on legs and joints. It works by neutralizing free radicals, suppressing inflammatory signaling molecules, and carrying other medications through the skin. While it’s widely used in equine practice, proper handling matters because DMSO pulls anything on the skin’s surface directly into the bloodstream.
What DMSO Does in the Body
DMSO reduces inflammation through several pathways at once. It scavenges free radicals, the unstable molecules that damage cells during an inflammatory response, and it does this in a dose-dependent way: more DMSO neutralizes more radicals. It also blocks the production of prostaglandin E2, a compound that drives pain and swelling at injury sites, and lowers levels of pro-inflammatory cytokines that amplify the immune response.
The other property that makes DMSO unique is its ability to cross biological membranes easily. This means it penetrates skin and carries dissolved substances with it. Veterinarians use this “carrier” effect to deliver other medications, like corticosteroids or antibiotics, through the skin without injections. But this same property is exactly why safe handling is so important.
Common Uses in Horses
The most frequent use is managing joint inflammation and osteoarthritis, a leading cause of dysfunction and economic loss in horses. DMSO is applied topically over swollen joints, tendons, and soft tissue injuries to reduce acute inflammation. Veterinarians also use it as part of joint lavage procedures for synovitis.
Beyond joints, DMSO is used intravenously in clinical settings for more serious conditions. For acute laminitis, it may be given as an IV solution at 0.1 to 1.0 g/kg of body weight, diluted to a 10% solution and administered every 8 to 24 hours for up to five days. IV use is strictly a veterinary procedure, not something to attempt on your own. DMSO also sees use in cases involving brain or spinal cord swelling, where its ability to reduce tissue edema can be critical.
How to Apply DMSO Topically
Before applying DMSO to your horse’s skin, the area needs to be completely clean. Wash and dry the application site thoroughly. Any dirt, fly spray, liniment residue, or topical product on the skin will be driven into the tissue along with the DMSO. This is the single most important safety step: a clean application site prevents contaminants from being absorbed into the bloodstream.
DMSO is available in liquid, gel, and ointment forms. Gel tends to be the easiest to work with for topical use on horses because it stays in place and doesn’t run. Apply the product directly to the skin using clean or sterile cotton, not your bare hands. Spread a thin, even layer over the affected area. More is not better; a thick coating increases the chance of skin irritation without improving results.
After application, keep your horse from rolling or rubbing the treated area for at least 20 minutes to allow absorption and prevent the horse from ingesting the product. If you’re wrapping the area, use a clean bandage and make sure nothing underneath the wrap could be carried into the skin by the DMSO.
Choosing the Right Grade
DMSO comes in different purity grades, and this matters. Veterinary-grade or pharmaceutical-grade DMSO (typically 90% to 99% pure) is what you want. Industrial or solvent-grade DMSO may contain impurities that you cannot see or smell, and because DMSO pulls substances through biological membranes so effectively, those contaminants will be absorbed directly into your horse’s tissues. Never substitute an industrial product to save money. Look for products specifically labeled for veterinary or medical use.
Glove Selection and Handler Safety
DMSO crosses human skin just as easily as it crosses your horse’s. If you have any substance on your hands when you touch DMSO, it will be absorbed into your own body. This makes glove choice critical, and not all gloves are equal.
Butyl rubber, fluoroelastomer, or neoprene gloves provide reliable protection. Thick latex gloves (15 mil or heavier) also work. Standard nitrile gloves, the kind most people keep in their barn, may protect against brief, incidental contact but degrade rapidly with sustained DMSO exposure. If nitrile is all you have, double-glove and change them frequently. Do not rely on thin disposable nitrile for a full application session.
If DMSO contacts your skin, you’ll likely notice a garlic or oyster-like taste in your mouth within minutes. This happens because the body converts DMSO into a volatile byproduct called dimethyl sulfide, which is exhaled through the lungs. It’s harmless but unsettling, and it confirms that absorption has occurred.
Side Effects to Watch For
The most common reaction in horses is local skin irritation. Roughly 15% to 16% of subjects in clinical studies develop a burning or stinging sensation at the application site, and a similar percentage experience skin dryness, scaling, or peeling. These reactions are more likely with repeated daily use or higher concentrations. If your horse’s skin becomes red, flaky, or obviously uncomfortable, reduce the frequency of application or dilute the DMSO with sterile water.
Garlic breath is nearly universal and harmless. It can persist for a day or two after application and is simply the body processing the compound.
More serious systemic reactions are uncommon with topical use but have been documented with higher doses and IV administration. These include changes in blood pressure, slowed heart rate, and in rare cases respiratory symptoms. If your horse seems unusually lethargic, has labored breathing, or shows signs of distress after DMSO use, contact your veterinarian.
Storage and Handling Tips
Pure DMSO has a freezing point of about 65°F (18.5°C), which means it can solidify in an unheated barn during cooler months. If your DMSO crystallizes or turns solid, warm it gently at room temperature or in a warm water bath. Don’t microwave it or heat it on a stove. The compound isn’t damaged by freezing and thawing, so crystallization doesn’t mean the product has gone bad.
Store DMSO in its original container, tightly sealed, away from other chemicals. Because of its solvent properties, DMSO can leach compounds from certain plastics. Glass or HDPE (high-density polyethylene) containers are safest for long-term storage. Keep it out of direct sunlight and away from sources of contamination.
Competition and Withdrawal Times
DMSO is a controlled substance under both USEF and FEI rules. The FEI includes it on its prohibited substances list, meaning any horse competing at FEI-sanctioned events must observe a withdrawal period before competition. Specific detection times are published by the FEI and updated periodically, so check the current list before any event. USEF rules similarly regulate DMSO, and detection thresholds can vary by organization and discipline.
If your horse competes, keep a treatment log that includes dates, amounts, and application method. A positive test for DMSO can result in disqualification and penalties even if the intent was purely therapeutic. When in doubt, consult your veterinarian about appropriate withdrawal windows for your specific competition schedule.