DMSO is a simple organosulfur compound (C₂H₆OS) that holds a complex place in industrial chemistry and medical history. This colorless liquid is recognized as a powerful and highly versatile solvent, capable of interacting with a wide range of substances.
Its unique chemical properties allow it to perform functions in the laboratory and the body that few other compounds can match. The history of its medical investigation is marked by periods of enthusiasm, controversy, and strict regulatory oversight. This dual identity makes DMSO a fascinating subject, straddling the line between a common laboratory reagent and a specialized pharmaceutical agent.
Chemical Identity and Unique Solvent Properties
DMSO is structurally defined by its sulfoxide functional group: a sulfur atom double-bonded to an oxygen atom, with two methyl groups attached. This arrangement results in a highly polar molecule with a significant separation of charge. Since the hydrogen atoms on the methyl groups are not acidic and cannot participate in hydrogen bonding, DMSO is classified as a polar aprotic solvent.
This nature provides exceptional solvency, allowing it to dissolve both highly polar and non-polar compounds, earning it the reputation of a “universal solvent.” It is completely miscible with water and a large number of organic solvents, a valuable property in chemical and biological applications. Pure DMSO has a melting point of approximately 18.5°C (65.3°F), meaning it solidifies near room temperature. This high freezing point often requires users to warm the container to return it to a liquid state.
Established Medical and Laboratory Applications
DMSO’s ability to penetrate biological membranes and interact with water molecules has secured its place in two distinct, regulated applications: medicine and cryopreservation.
In human medicine, the FDA has given limited approval for its use in treating interstitial cystitis (IC), a chronic bladder condition. The pharmaceutical preparation, marketed as Rimso-50, is a 50% aqueous solution. Treatment involves intravesical instillation, where the solution is delivered directly into the bladder via a catheter. Although the exact mechanism is not fully understood, DMSO is thought to provide relief by reducing inflammation, relaxing the smooth muscle of the bladder wall, and providing direct analgesic effects. This specialized use remains the only FDA-approved human therapeutic application.
In laboratory science, DMSO is an indispensable component in the cryopreservation of biological materials, including stem cells, blood, and tissue samples. The compound acts as a cryoprotectant by penetrating the cell membrane and interacting with intracellular water. This intervention colligatively depresses the freezing point of the cell’s internal environment. By stabilizing the cell structure, DMSO prevents the formation of large, damaging ice crystals that would otherwise puncture the cell walls and organelles, maintaining viability during long-term storage in liquid nitrogen. A typical concentration for this purpose is between 5% and 10% DMSO in the freezing medium.
Understanding DMSO’s Biological Actions
The effects of DMSO on living systems stem from its unique capacity to rapidly traverse biological barriers. Its small size and amphipathic nature allow it to quickly cross the skin and cellular membranes, making it an effective transdermal delivery vehicle. This characteristic enables DMSO to function as a penetration enhancer, carrying other dissolved substances across the skin and into the systemic circulation.
Once inside the body, DMSO exhibits anti-inflammatory and antioxidant properties. It operates as an effective scavenger of free radicals, particularly the highly reactive hydroxyl radical, a major contributor to cellular damage and inflammation. By neutralizing these molecules, DMSO can help mitigate the secondary injury that often accompanies tissue trauma and ischemia.
The compound also exhibits analgesic effects, thought to be a direct result of its influence on nerve function. Studies show that DMSO can effectively block conduction in peripheral nerve C fibers, the neurons responsible for transmitting pain signals. At concentrations around 9% or higher, the compound can slow or completely block the transmission of these pain impulses, providing a localized numbing effect.
Regulatory Status, Off-Label Use, and Safety Profile
The regulatory landscape for DMSO is marked by a sharp division between its approved and its widespread, often unregulated, applications. The FDA maintains approval solely for treating interstitial cystitis in humans and for topical use in veterinary medicine to treat acute swelling due to trauma in animals like horses and dogs. However, due to its accessibility and perceived therapeutic effects, non-pharmaceutical-grade DMSO is frequently used off-label by the public for various musculoskeletal and inflammatory conditions.
This common off-label use introduces substantial safety concerns, primarily related to product purity. Industrial-grade DMSO, often sold in hardware or feed stores, may contain toxic impurities or heavy metals that are harmless in a non-biological context but become dangerous when absorbed. Because of DMSO’s powerful carrier function, any contaminants in the solution or on the skin are rapidly transported across the skin barrier and into the bloodstream.
The most common side effect following the use of DMSO is the distinctive garlic- or oyster-like odor that is excreted through the breath and skin. This odor is caused by the metabolic breakdown of DMSO into its volatile metabolite, dimethyl sulfide (DMS). While generally harmless, this characteristic odor can persist for up to three days after application. Other potential adverse effects include localized skin irritation, redness, or a burning sensation at the application site, and in rare cases, systemic allergic reactions.