Isopropyl alcohol (isopropanol) is the primary active ingredient in the product sold commercially as rubbing alcohol. The difference between them is nomenclature and composition: isopropyl alcohol is the pure chemical compound, while rubbing alcohol is a solution formulated for consumer use. Rubbing alcohol is standardized to contain a specific concentration of isopropanol mixed with water and sometimes other additives.
Understanding the Difference in Names
Isopropyl alcohol (IPA) is a specific chemical compound, a colorless, flammable liquid. The term “rubbing alcohol” is a commercial designation for a solution intended for topical application. In the United States, “isopropyl rubbing alcohol” is defined by the United States Pharmacopeia (USP) as a solution containing approximately 70% by volume of pure isopropanol. This regulatory standard ensures the commercial product meets criteria for purity and consistency.
Rubbing alcohol solutions must contain specific components to comply with safety standards. They are required to include a bittering agent, such as denatonium benzoate, to make the product unpalatable and prevent accidental ingestion. This denaturing process renders the mixture toxic for consumption, distinguishing it from beverage alcohol (ethanol). While most rubbing alcohol uses isopropanol, the term “rubbing alcohol” refers to the product formulation rather than the single chemical.
Concentration Levels and Required Additives
Isopropyl alcohol is sold over the counter in various concentrations, most commonly 70%, 91%, or 99%, with the remaining percentage being water. The concentration level significantly affects the product’s function, particularly its effectiveness as a disinfectant. The 70% solution is generally the most effective germicide because the water content is an integral part of the process.
Water acts as a catalyst, slowing evaporation and allowing the alcohol to penetrate the cell walls of microorganisms. High-concentration alcohol, such as 91% or 99%, instantly coagulates the proteins on the outside of the microbial cell. This rapid coagulation creates a protective layer that shields the rest of the cell, allowing the organism to survive. The 70% solution penetrates the cell wall more completely, coagulating all internal proteins and successfully killing the organism.
Higher concentrations, like 99% isopropyl alcohol, are better suited for uses requiring minimal water and quick evaporation. These purer forms are excellent for cleaning sensitive electronics or removing sticky residues because they evaporate rapidly without leaving moisture. However, for disinfecting surfaces or skin, the 70% concentration is superior due to the presence of water.
Safe and Practical Applications
The most common household use for isopropyl alcohol solutions is as a topical antiseptic for minor cuts and scrapes or for preparing skin before an injection. The 70% concentration is recommended for this purpose, offering the optimal balance of germicidal effectiveness and gentleness on the skin. It is also highly effective for general surface disinfection, such as cleaning high-touch areas.
The quick evaporation rate of isopropyl alcohol makes it a popular choice for cleaning and removing residues without leaving streaks. Applications include:
- Cleaning electronics.
- Removing grease, oil, and adhesives.
- Cleaning makeup brushes.
- Deodorizing shoes or removing permanent marker stains.
All concentrations are volatile and highly flammable, requiring storage away from heat or open flames.
Safety precautions are necessary since isopropyl alcohol is poisonous if ingested and must only be used externally. Prolonged inhalation of its vapors should be avoided by ensuring adequate ventilation during use. Applying it to large areas of broken skin is also discouraged, as the body can absorb toxic amounts.