Isopropyl alcohol (IPA), also known as propan-2-ol, is a colorless, flammable chemical compound common in many household products. It is most recognized as the active component in “rubbing alcohol,” typically sold in 70% or 91% aqueous solutions. The question of whether IPA “burns” has two distinct meanings: the chemical’s ability to combust and catch fire, or the sensation of irritation and stinging it causes upon contact with the skin. Understanding both aspects is necessary for safe handling and storage.
The Science of Ignition
Isopropyl alcohol is classified as a highly flammable liquid, meaning it ignites easily under normal conditions. The primary factor determining its fire risk is its low “flash point,” which is the minimum temperature at which the liquid produces enough vapor to form an ignitable mixture with the air. Pure IPA has a flash point of approximately 53°F (12°C). This means that at or above typical room temperature, it is constantly releasing flammable vapors. Any ignition source, such as a spark, an open flame, or a hot surface, can cause a fire if it comes into contact with these vapors. The flammability risk is also dependent on the concentration of the alcohol. Rubbing alcohol is diluted with water, which acts as a fire retardant by absorbing heat.
Common 70% IPA solutions contain enough water to make ignition slightly more difficult than pure forms. Higher concentrations, like 91% or 99% IPA, contain significantly less water and are more volatile and easier to ignite. These higher concentrations evaporate faster and release a greater volume of flammable vapor into the surrounding air, increasing the fire hazard. The vapors are also heavier than air, meaning they can travel along surfaces to an ignition source and flash back to the liquid’s container.
Topical Effects on Skin
When applied to the skin, isopropyl alcohol does not cause a chemical burn. The “burning” or stinging sensation often felt, particularly on broken skin, is a neurological response. Alcohol molecules interact with specific nerve receptors, such as the VR1 receptor, which detects heat and pain. This interaction lowers the temperature threshold at which these receptors fire signals to the brain, creating a sensation of heat or stinging even though no thermal burn has occurred.
The cooling sensation experienced when IPA is applied is due to its rapid evaporation from the skin’s surface, which draws heat away quickly. This rapid evaporation contributes to the chemical’s dehydrating effect. IPA is an effective solvent that strips away the natural protective oils, known as sebum, from the skin’s outer layer. Removing these oils compromises the skin barrier, leading to dryness, cracking, and irritation. Repeated exposure can cause contact dermatitis, making IPA unsuitable for routine use as a hand sanitizer.
Safe Usage and Storage Guidelines
Proper handling of isopropyl alcohol is necessary due to its high flammability and potential for skin irritation. When using IPA, particularly in higher concentrations, it is important to work in a well-ventilated area. Good airflow helps to disperse the heavy, flammable vapors, preventing them from accumulating to a dangerous concentration. Users should always ensure there are no ignition sources nearby, including open flames, sparks, cigarettes, or operating electrical equipment.
Storage must prioritize minimizing fire risk and preventing accidental exposure. IPA should be kept in its original, tightly sealed container to prevent the release of flammable vapors and reduce evaporation. The container should be stored in a cool, dry, and well-ventilated location, away from direct sunlight or any sources of heat. For personal safety, IPA should never be ingested, as it is toxic and can cause serious internal damage. When applying it topically, avoid sensitive areas like the eyes, where it can cause significant irritation. If accidental eye contact or prolonged skin irritation occurs, the area should be flushed immediately with water, and medical attention may be necessary.