Why is 70% Isopropyl Alcohol Better Disinfectant than 99% Isopropanol

Why Is 70% Isopropyl Alcohol (IPA) a Better Disinfectant than 99% Isopropanol, and What Is IPA Used For ?

Isopropyl alcohol (2-propanol), also known as isopropanol or IPA, is the most common and widely used disinfectant within pharmaceutics, hospitals, cleanrooms, and electronics or medical device manufacturing. Different solutions, purity grades, concentrations, and alcohol types yield beneficial cleaning and disinfection properties when applied correctly; or dangerous consequences when used improperly. This post will help you identify key uses, best practices, and proper disinfection with isopropyl alcohol. Likewise you can see our other posts on IPA as a universal cleaner and the importance of high-quality USP IPA.

Why Is 70% the Most Effective Concentration of Isopropyl Alcohol for Disinfection?

Isopropyl alcohol, particularly in solutions between 60% and 90% alcohol with 10 – 40% purified water, is rapidly antimicrobial against bacteria, fungi, and viruses. Once alcohol concentrations drop below 50%, usefulness for disinfection drops sharply. Notably, higher concentrations of alcohol don’t generate more desirable bactericidal, virucidal, or fungicidal properties.

The presence of water is a crucial factor in destroying or inhibiting the growth of pathogenic microorganisms with isopropyl alcohol. Water acts as a catalyst and plays a key role in denaturing the proteins of vegetative cell membranes. 70% IPA solutions penetrate the cell wall more completely which permeates the entire cell, coagulates all proteins, and therefore the microorganism dies. Extra water content slows evaporation, therefore increasing surface contact time and enhancing effectiveness. Isopropyl alcohol concentrations over 91% coagulate proteins instantly. Consequently, a protective layer is created which protects other proteins from further coagulation.

Solutions > 91% IPA do kill bacteria, but sometimes require longer contact times for disinfection, and enable spores to lie in a dormant state without being killed. In this analysis, a 50% isopropyl alcohol solution kills Staphylococcus Aureus in less than 10 seconds (pg. 238), yet a 90% solution with a contact time of over two hours is ineffective. Some disinfectants will kill spores, which are classified as chemical sterilants. So why do higher alcohol solutions yield fewer results for bactericidal and antimicrobial outcomes?

Why Doesn’t Isopropyl Alcohol Kill Bacteria and Fungal Spores?

Some bacteria transform into spore cells when external conditions are unfavorable; the result is reduced metabolic activity, higher ‘cidal’ resistance, and immunity from alcohol-based disinfectants. Spores lie dormant, and once conditions become favorable again, the microbe converts back to a vegetative state and grows actively. When examining the effectiveness of IPA, accurately translating its benefits and shortcomings require distinctions of identity, purity, sterility, and intended use. Disinfection, unlike sterilization, does not provide sporicidal attributes.

Isopropyl alcohol is excluded from classification as a high-level disinfectant because of its inability to eradicate bacterial spores and hydrophilic viruses such as polio. Its low-level categorization outlines effectiveness for noncritical patient care devices such as blood pressure cuffs. IPA is also commonly applied during cleanroom wipedown for disinfecting tools and packaging that must pass into ultra-clean spaces.

Why Not Use Higher Isopropyl Alcohol (91%+) Concentrations?

70% isopropyl alcohol upholds key requirements for use as a bactericidal in cleanrooms or medical facilities, but also for general purposes. 70% IPA/30% water solutions produce less vapor and odor, therefore reducing risks of toxic fumes or combustion. When isopropyl alcohol reacts with air, light, and oxygen, it forms unstable peroxides which increase the likeliness of explosion, especially when heated with aluminum. IPA volatility increases with storage time and alcohol concentration, especially when exposed to light over multiple years after opening.

70% IPA is less flammable but also offers a more economical price point for general wipe down and large-surface disinfection. Likewise, high-moisture alcohols evaporate slower and increase contact time without becoming immediately dry. If 70% IPA is so effective as both a general-purpose cleaner and disinfectant, why use 99% concentrations?

When Is 99% Isopropyl Alcohol Used?

99% isopropyl alcohol is ideal as a solvent or cleaning agent for industries that produce water sensitive items, therefore rapid evaporation and low water content is favorable. 99% USP IPA provides the lowest presence of water and in some forms is free from denaturants. Computer technicians, medical device manufacturers, printed circuit board manufacturers, and soldering and rework technicians prefer immediate evaporation for work with sensitive devices such as integrated circuit adapters, computer chips, and circuit boards. 99% IPA evaporates cleanly and minimizes residual substances. Rapid evaporation reduces shelf life but is more effective against sticky residues, grease, and grime than 70% concentrations. Because isopropanol is hygroscopic, acetone may yield better grime fighting results for inks or oils.

Is Isopropyl Alcohol Effective Against Fungus and Fungal Spores?

Isopropyl alcohol may be intermittently effective against fungus but it is not effective against fungal spores. Treatment of mold and fungus is generally considered a problem of moisture and humidity. Applying a surface level cleaner may have little or no effect on fungal removal. Bleach and hydrogen peroxide are more commonly associated with remedying mold and fungus outbreaks.

Officially, government organizations are somewhat conflicted on the use of bleach for mold.

The EPA does not recommend bleach.

The CDC recommends bleach as part of a mold remediation effort.

What’s the Difference Between Types of Isopropyl Alcohol?

What Is USP-Grade Isopropyl and What Is It Used For?

The United States Pharmacopeial Convention (USP) is a nonprofit scientific organization that develops and disseminates public quality standards for medicines, food, and supplements. USP-grade isopropyl alcohol certification ensures that both the isopropyl alcohol and any additives are of the highest purity, potency, and accurate concentration. Manufacturing, packaging, and storage must adhere to strict guidelines, and all production facilities must uphold FDA registration and inspection. These specifications improve consistency and safety for industrial, pharmaceutical, flavor & fragrance, or lab use.

What is NSF Grade Isopropyl Alcohol?

The National Sanitation Foundation (NSF) is a non-government, nonprofit organization that independently focuses on public health and safety of food industries, water supplies, consumer products, and human environments. Strict standards include product testing and material analyses in every aspect of a product’s development. NSF certification involves regular on-site inspections of manufacturing facilities and regular retesting of products. If a product fails to meet benchmarks, the NSF enforces actions including recall, public notification, or even de-certification.

What Is Pure Isopropyl Alcohol?

Pure isopropyl alcohol is manufactured and processed without common additives such as denaturants, which make the alcohol unfit for human consumption. Pure isopropyl alcohol is not interchangeable with sterile or USP-grade isopropyl alcohol, but misnomers occur frequently because USP-grade alcohol is always in a pure state.

What Is Industrial Grade Alcohol?

Industrial grade isopropyl alcohol, also referred to as technical grade isopropyl alcohol, is used most commonly for non-critical manufacturing and processing purposes such as removing ionic salts from PCBs, thermal paste from heat sinks and IC packages, or dissolving the organic acids in rosin-based soldering fluxes. It’s an economic option for sanitation of large surface areas, and mitigation of general contaminants such as dust, debris, grease, and adhesives present from other manufacturing processes.

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