What is DMSO (Dimethyl Sulfoxide)?
Dimethyl Sulfoxide, commonly known as DMSO, is a chemical solvent that originates as a by-product of the paper-making process [1.3.2]. It is a clear liquid known for its unique and powerful ability to penetrate biological membranes like the skin with ease [1.3.4, 1.4.1]. This property allows it to not only be absorbed rapidly itself but also to carry other substances dissolved within it directly into the body's systems [1.2.2].
This transdermal delivery mechanism is central to both its limited medical applications and its significant risks. While it has been explored for various uses since the mid-20th century, its approved applications remain very narrow due to safety concerns and a lack of robust scientific evidence for many of its purported benefits [1.3.2, 1.8.5].
Approved and Off-Label Uses
The only use for DMSO that is officially approved by the U.S. Food and Drug Administration (FDA) is as a prescription medication, branded Rimso-50, for the treatment of interstitial cystitis, a chronic bladder pain syndrome [1.3.1, 1.3.3]. In this procedure, a purified, medical-grade solution is instilled directly into the bladder [1.3.1].
In veterinary medicine, DMSO is used topically in products like liniments for horses to reduce inflammation and swelling [1.5.2]. It is also widely available as an industrial-grade solvent, which is not intended for any biological use [1.2.2, 1.5.3]. Despite the lack of approval, it is anecdotally used and promoted for a wide array of human ailments, including arthritis, pain relief, and shingles, though scientific evidence supporting these uses is weak or non-existent [1.3.2, 1.3.6].
The Critical Difference: Pharmaceutical-Grade vs. Veterinary-Grade DMSO
The most significant danger in using horse liniment on humans lies in the grade of the DMSO. There are three primary grades: industrial, veterinary, and pharmaceutical (medical) [1.5.3]. The distinction is not trivial; it's a matter of safety and purity.
- Pharmaceutical-Grade DMSO (USP-grade): This is the only grade approved for human use [1.3.1]. It is highly purified and regulated to ensure it is free from contaminants [1.5.4]. It's available only by prescription for its specific approved use [1.3.1].
- Veterinary-Grade DMSO: This is what is found in horse liniments. It is not regulated for human use and can contain a variety of impurities and other unlisted active ingredients [1.2.2, 1.2.6].
- Industrial-Grade DMSO: This version is used as a solvent, cleaner, or paint thinner [1.2.3]. It can be contaminated with toxic substances like pesticides, acetone, and other chemicals [1.5.3, 1.4.2].
Below is a comparison highlighting the critical differences:
| Feature | Pharmaceutical-Grade DMSO | Veterinary/Industrial-Grade DMSO |
|---|---|---|
| Purity | High purity (e.g., 99.9%+) and tested to be free of contaminants [1.5.4]. | Purity is unknown and may contain dangerous impurities like acetone, acids, or other solvents [1.2.3, 1.5.3]. |
| Regulation | Regulated by the FDA for a specific human medical condition [1.3.1]. | Not regulated for human use. Formulations can vary widely [1.2.1, 1.2.2]. |
| Intended Use | Intravesical treatment for interstitial cystitis, under medical supervision [1.3.3]. | Topical anti-inflammatory for horses or as an industrial solvent [1.5.2]. |
| Safety for Humans | Considered safe only for its prescribed use by a healthcare professional [1.3.1]. | Considered unsafe and not recommended for human use due to the risk of absorbing toxins [1.4.1, 1.4.7]. |
Is DMSO Horse Liniment Safe for Humans? The Risks and Dangers
Using a non-prescription, veterinary-grade DMSO product on your skin is not safe [1.2.2]. The primary danger stems from its function as a solvent. Because DMSO so effectively carries other chemicals through the skin, any impurities present in the horse liniment will be transported directly into your bloodstream [1.4.1]. Industrial or veterinary products can be contaminated with toxic substances from the manufacturing process, and you have no way of knowing what you are absorbing [1.4.2, 1.5.3].
Known Side Effects and Health Risks
Even when using pure DMSO, there are numerous potential side effects. The most universally reported one is a distinctive garlic-like taste in the mouth and a garlic-like body and breath odor, which can appear within minutes of application and last for up to 72 hours [1.3.1, 1.6.4].
Other common side effects from topical application include [1.4.1, 1.6.5]:
- Skin irritation, including redness, itching, burning, and rashes
- Headaches
- Dizziness
- Nausea and stomach upset
More serious risks are associated with using impure products or high concentrations, including potential damage to the liver and kidneys and negative effects on blood cells [1.4.7, 1.4.5]. Furthermore, DMSO can increase the effects of other medications like blood thinners, steroids, and sedatives, leading to dangerous interactions [1.4.1, 1.4.4].
Unproven Claims vs. Scientific Reality
Many proponents claim DMSO is a miracle cure for conditions ranging from osteoarthritis to cancer, but these claims are not supported by robust scientific evidence [1.3.5, 1.8.5]. While some small studies have suggested it may have anti-inflammatory or pain-blocking properties, the results are often inconclusive or methodologically flawed [1.8.1, 1.8.6]. A 2009 study found that for knee osteoarthritis, DMSO was no more effective than a placebo in providing pain relief [1.8.5].
The difficulty in conducting reliable studies is compounded by DMSO's strong, tell-tale odor, which makes proper blinding (where neither the patient nor the researcher knows who is receiving the treatment versus a placebo) nearly impossible [1.3.5].
Conclusion: A Clear Verdict
Given the evidence, the answer is clear: it is not safe to use DMSO horse liniment on humans. The significant risk of absorbing unknown and potentially toxic contaminants from unregulated veterinary or industrial products far outweighs any unproven benefits [1.2.2, 1.4.1]. The only safe way to use DMSO is as a pharmaceutical-grade prescription product under the direct supervision of a healthcare professional for its single FDA-approved indication [1.3.1]. For any other aches, pains, or medical conditions, consult a doctor for proven and safe treatments.
For more information on the approved uses and risks of DMSO, you can consult authoritative sources like the Memorial Sloan Kettering Cancer Center [1.8.1].
