DMSO: What It Is, What It Is Used for and How to Store It

DMSO shows up in the same cupboards as Epsom salt and cayenne salve, usually in a brown glass bottle bought from a feed store or a supplement shelf. It's an industrial solvent with one unusual property: it goes through skin in minutes and takes whatever is dissolved in it along for the ride. That property is the whole story. It's why people rub it on a sore knee, why horse vets have used it on swollen legs for decades, and why the bottle has to be treated with more respect than a jar of liniment.

Dimethyl sulfoxide is a clear, slightly oily liquid recovered from the wood pulping process. It mixes with water in any proportion, has a faint sulfur smell, and melts at 18.5°C, which is 65°F; a bottle kept in a cool cupboard or a garage is often solid, and that is not spoilage. It is hygroscopic, meaning an open bottle pulls water out of the air and weakens itself. It's a mild skin and eye irritant on its own, combustible rather than flammable (flash point 87°C, 189°F), and with repeated contact it dries skin by stripping the oils out of it, the way any strong solvent does.

Three jobs. The first is the one it's sold for at the feed store: a topical liniment for horses and dogs to reduce swelling, which has been standard veterinary practice for a long time. The second is what people buy it for at the supplement shelf: rubbing it on sore muscles, arthritic joints and nerve pain. There is a prescription form of it that a urologist instills into the bladder, and that is the only use with a formal medical label; for everything else the evidence is thin and mostly personal report, and this page does not pretend otherwise. The third job is the shop: it dissolves many paints, adhesives and resins, so it strips a brush or lifts a label where acetone has failed, with the warning that it also softens some plastics, so test first.

Industrial or technical grade DMSO can carry whatever came through the process with it, and because DMSO carries dissolved things through skin, those contaminants go in too. Nothing but pharmaceutical grade, labeled USP and 99.9 percent or better, goes anywhere near skin. The industrial jug is a solvent for the shop and nothing else. The label should say the grade; if it does not, it is the shop jug.

Everything about applying DMSO follows from the one property. Wash the skin with soap and water first and dry it, because sunscreen, insect repellent, lotion, dye or anything else on that patch of skin is going in with it. Use clean bare hands or a clean cotton pad; nothing between the bottle and the skin that could dissolve into it. Most skin use is at 70 percent or lower, diluted with distilled water, because the full strength liquid burns, reddens and dries skin more; the vet gels run stronger and are made for hide, not skin. Try a small area first. Expect warmth, some redness and itching, and within minutes a garlic or oyster taste and breath that lasts hours, which is the body breaking it down into sulfur compounds; that taste is also the proof it went through. Keep it out of eyes, and do not put anything else on that skin until it has been washed. Serious allergic reactions are rare but real: breathing trouble, swelling of the face or throat, hives, dizziness. Stop and get help if any of those show up. Nobody knows what it does in pregnancy. Research before dosing yourself, and start with the smallest patch and the weakest mix.

DMSO reacts violently with strong oxidizers, strong acids and strong bases. In a preparedness cupboard that means the pool shock, the bleach, the muriatic acid and the lye all live on a different shelf, and the solvent never gets used to clean anything that has had them on it. It also means never applying it over a wound or a rash that has been treated with something else, and never mixing it into another liniment or salve on a guess. The never mix chart covers the oxidizers; the rule for DMSO is simpler: nothing is mixed with it that you would not want inside you.

Glass, amber if you have it, with the lid tight, in a cool dark cupboard away from the oxidizers. Stored that way it keeps for years; it's a stable chemical and the only things that degrade a bottle are water pulled in from the air and whatever leaches out of a soft plastic container. A frozen bottle is thawed in warm hands or a bowl of warm water, never on a stove. Label it with the grade and the date opened, keep it where children and animals cannot reach it, and keep the vet gel and the pharmaceutical bottle apart so the wrong one never gets used on a person.

Sources: the International Chemical Safety Card for dimethyl sulfoxide (physical properties, incompatibilities, storage) and standard drug references for the skin effects and the purity warning.