DMSO, or dimethyl sulfoxide, is a colourless, strongly polar organic liquid with the CAS number 67-68-5 and the molecular formula C2H6OS. Its most unusual property is that it penetrates intact skin readily and carries dissolved substances with it, which is why it appears both as an industrial reaction solvent and as a carrier in topical formulations. DMSO 70% is the aqueous dilution of that solvent: a solution of roughly seventy parts DMSO to thirty parts water, supplied ready to use. The dilution is neither decorative nor a way of cheapening the product. Pure DMSO freezes at 18.5 °C, so on a cool day a drum of neat material can be a solid block. Water depresses that freezing point sharply, so the 70% solution stays pourable and pumpable in unheated warehouses and remains far easier to meter into a process.
Physical and Chemical Properties
| Property | Value |
|---|---|
| Chemical name | Dimethyl sulfoxide |
| CAS number | 67-68-5 |
| Molecular formula | C2H6OS |
| Molar mass | 78.13 g/mol |
| Appearance | Colourless liquid |
| Relative density | about 1.10 at 20 °C |
| Boiling point | 189 °C |
| Melting point | 18.5 °C |
| Refractive index | 1.477 at 20 °C |
| Dipole moment | about 3.96 D |
| Water solubility | miscible with water in all proportions |
DMSO is a polar aprotic solvent: it dissolves salts, sugars and many polar organic compounds without donating or accepting protons. It is also strongly hygroscopic, so open containers take up atmospheric moisture and the concentration of an unsealed batch drifts upwards in water content over time. Dilution with water releases heat, which is normal but means water should be added to DMSO slowly, with stirring and cooling, rather than the other way round in a closed vessel.
Why DMSO Is Supplied as a 70% Solution
Handling: the mixed solution remains liquid well below 18.5 °C, so pumps, drums and dosing lines do not need heating.
Fixed strength: a ready-made 70% stock removes on-site dilution errors for users who work at a fixed dilution.
Reduced skin risk: the neat solvent penetrates skin quickly; a diluted stock lowers the amount of DMSO that can be absorbed during routine handling.
Process consistency: customers who need a defined water content can buy it in the product rather than adding it in the plant.
Because "70%" can be read on a weight or on a volume basis, buyers should establish which convention a supplier uses before specifying a formulation, since the two differ slightly in density and in final concentration.
Carrier and Penetration-Enhancer Applications
The best-known use of DMSO is as a vehicle that carries other substances through the skin barrier. In veterinary and topical product development it is used to dissolve an active ingredient and then to help it cross the stratum corneum, so that a lower loading of active can be used for the same effect. Formulations that exploit this property include topical anti-inflammatory and analgesic preparations, and vehicle systems in pharmacological research where a test compound has to reach tissue beneath the skin. The same property is a hazard as well as a benefit: anything dissolved in DMSO will also be carried through skin, so incompatible or toxic solutes must never be combined with it, and operators must avoid skin contact with the solution.
Cryopreservation and Laboratory Use
DMSO is the classic cryoprotectant for biological material. It reduces ice-crystal damage during freezing and thawing of cells and tissue, and it is a standard component of freezing media in cell banks and research laboratories. A concentrated aqueous stock is convenient for these users because working strength media are then prepared by simple dilution with culture medium or buffer. DMSO is also widely used as a solvent in organic synthesis, including oxidation reactions and polymer processing, where its high boiling point, high polarity and aprotic character allow reactions that would not run in water or in alcohols.
Industrial and Formulation Uses
| Application area | Function of DMSO or DMSO 70% |
|---|---|
| Agrochemical formulations | Solvent and carrier for active ingredients; improves uptake on treated surfaces |
| Industrial cleaning | High-polarity solvent for polar soils, resins and burnt-on deposits |
| Paint and coating removal | Softens polymer films as a component of slow-evaporating strippers |
| Chemical synthesis | Polar aprotic reaction medium and oxidant-activating solvent |
| Polymer and fibre processing | Solvent for spinning solutions and for difficult-to-dissolve polymers |
Where a formulation already needs another polar aprotic solvent, DMSO is frequently compared with the alternatives below, all of which are higher in cost or carry their own handling constraints.
| Co-solvent | CAS number | Typical role |
|---|---|---|
| Dimethyl sulfoxide | 67-68-5 | Polar aprotic solvent, penetration enhancer |
| N,N-Dimethylformamide | 68-12-2 | Polar aprotic reaction solvent |
| N,N-Dimethylacetamide | 127-19-5 | Polar aprotic solvent for polymers and fibres |
| N-Methyl-2-pyrrolidone | 872-50-4 | High-boiling solvent for resins and coatings |
| Acetonitrile | 75-05-8 | Medium-polarity solvent for analysis and synthesis |
Safety, Contact Control and Material Compatibility
Skin: DMSO crosses skin rapidly and carries dissolved substances with it. Wear butyl rubber or laminated-film gloves and protective clothing; thin nitrile gloves alone are not adequate for prolonged or repeated contact.
Moisture: keep containers closed. The product is hygroscopic, and an open drum will pick up water and change concentration.
Materials: glass, stainless steel, PTFE and polyethylene are suitable for storage and transfer. Some engineering plastics, including polycarbonate, are attacked or swollen by DMSO, so gaskets, seals and tubing should be checked against supplier compatibility data.
Reactivity: keep away from strong oxidising agents and from acid chlorides, and avoid uncontrolled mixing with water in closed vessels because dilution releases heat.
Grade: material intended for pharmaceutical or veterinary use must be supplied as a documented grade with the relevant purity, residual solvent and water data, and used within the applicable regulatory approvals.
Frequently Asked Questions
Q: What is DMSO 70% used for?
It is used as a ready-to-use polar aprotic solvent: as a carrier and penetration enhancer in topical and veterinary formulations, as a cryoprotectant stock in laboratories, and as a high-boiling solvent in synthesis, agrochemical and industrial cleaning applications.
Q: What is the CAS number of DMSO?
The CAS number of dimethyl sulfoxide is 67-68-5, and its molecular formula is C2H6OS with a molar mass of 78.13 g/mol.
Q: Why is DMSO sold as a 70% aqueous solution instead of neat?
Pure DMSO freezes at 18.5 °C, so it can solidify in an unheated store. Diluting it with water lowers the freezing point, keeps the product liquid and pumpable, and gives users a fixed dilution that is easier to dose.
Q: Is DMSO soluble in water?
Yes. DMSO is miscible with water in all proportions and forms a clear, homogeneous solution at any ratio, while releasing heat on mixing.
Q: Can DMSO be handled with ordinary nitrile gloves?
Not for repeated or prolonged contact. DMSO penetrates many thin polymer gloves; butyl rubber or laminated-film gloves with a protective outer layer are the appropriate choice, together with eye protection and ventilation.
Q: What happens if a drum of DMSO is left open?
The solvent absorbs moisture from the air, so its water content rises and the stated concentration is no longer accurate. Containers should be resealed immediately after use and stored in a dry area.