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

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

What Is Isopropyl Alcohol and How Is It Used?

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.

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

Isopropyl alcohol, particularly in solutions between 60% and 90% alcohol and 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 may kill some bacteria, but require longer contact times for disinfection, and enable spores to lie in a dormant state without being killed. 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 with exposures times that exceed 3-12 hours, 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.

Is Sterilization with Isopropanol (AKA Isopropyl Alcohol or IPA) Possible?

Proper Uses of Isopropyl Alcohol Require Distinction Between Sterilization and Disinfection

Terms like disinfection and sterilization are often misunderstood and used interchangeably. The Center for Disease Control (CDC) defines terminology clearly:

Unlike sterilization, disinfection is not sporicidal. A few disinfectants will kill spores with prolonged exposure times (3–12 hours); these are called chemical sterilants. At similar concentrations but with shorter exposure periods (e.g., 20 minutes for 2% glutaraldehyde), these same disinfectants will kill all microorganisms except large numbers of bacterial spores; they are called high-level disinfectants. Antiseptics are germicides applied to living tissue and skin; disinfectants are antimicrobials applied only to inanimate objects. In general, antiseptics are used only on the skin and not for surface disinfection, and disinfectants are not used for skin antisepsis because they can injure skin and other tissues. Virucide, fungicide, bactericide, sporicide, and tuberculocide can kill the type of microorganism identified by the prefix. For example, a bactericide is an agent that kills bacteria.

— CDC

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% IPA
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 not only 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% IPA provides the lowest presence of adulterants and 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 ensures unchanging alcohol concentration. Alcohol evaporates faster than water when exposed to air; over time the alcohol concentration is diluted by excess water which yields unpredictable effectiveness and results. This degradation is avoided with pure isopropyl alcohol. It’s more effective against sticky residues, grease, and grime than 70% concentrations, but because isopropanol is hygroscopic, acetone may yield better grime fighting results.

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 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 discourage 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 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 disinfection of large surface areas, and mitigation of general contaminants such as dust, debris, grease, and adhesives present from other manufacturing processes.

What is Food Grade Alcohol?

The use of isopropyl alcohol for products fit for human consumption is limited. Generally, ethyl alcohol is preferred for consumable products, as it is GRAS (generally regarded as safe). For food grade products, FCC (Food Chemicals Codex) accreditation establishes acceptable levels of purity and ingredient quality for products intended for human consumption. Isopropyl alcohol use is most commonly found during the preparation of food flavorings, fragrances, fats, oils, colorants, preservatives, sweetners, and probiotics. 

What is Anhydrous Alcohol? Is Anhydrous Alcohol the Same as 99%?

Anhydrous simply means that a solution contains no water, and generally is of 99%+ concentration. Isopropyl alcohol that is 100% free of water is not feasible as it immediately absorbs water after exposure to humid air. High quality anhydrous alcohols produce a purity of +99.96%. 

What is Denatured Alcohol?

Denatured alcohol contains an adulterant that renders the solution undrinkable. Sometimes the additive is scented which can reduce the nausea and odors associated with alcohol vapors. While some online stores may market their products as “100% pure denatured isopropyl alcohol”, this is a misnomer. Pure isopropyl alcohol does not contain any denaturants. 

What Is Sterile Isopropyl Alcohol?

Sterile Isopropyl Alcohol meets the highest standards of purity in aseptic environments. Sterile certification ascertains 0.22-micron filtering, gamma irradiation between 25kGy – 50kGy and compliance of modified AAMI/ANSI/ISO 11137:2006 guidelines. Sterile IPA is packaged in a cleanroom and commonly used within the same environment for wipe down of pass-throughs, cleanroom furniture, laminar flow hoods, cleanroom furniture, and tables or work surfaces.

MSDS spec sheets for sterile isopropyl alcohol 

Is Isopropyl Alcohol the Same as Rubbing Alcohol?

Rubbing alcohol is an antiseptic, which U.S. Pharmacopeia standards defines as containing not less than 68% and not more than 72% of isopropyl alcohol. The remaining volume consists of water, with or without suitable stabilizers, perfume oils, and color additives certified by the FDA for use in drugs. The difference between rubbing alcohol and more pure forms of isopropyl alcohol is that rubbing alcohol contains denaturants which make the solution unpalatable for human consumption. Technically, all grades of rubbing alcohol containing 68% -72% isopropyl alcohol fall under the “rubbing alcohol” namesake for household use. Isopropyl alcohol concentrations >91% volume fail to provide bactericidal efficiency and are less effective for antiseptic use, thus its distinction as “rubbing alcohol” is not warranted and may cause confusion.

For more information, continue with the suggested reading below, or contact us about ordering in bulk, hazmat requirements, or for further questions on best usage and results.

Where Can I Buy 70% and 99% Isopropyl Alcohol?

Where to Buy 99% Isopropyl Alcohol by the Gallon
99% USP IPA Gallon

USP Grade 99%
Isopropyl Alcohol IPA Gallon

Where to Buy 70% Isopropyl Alcohol by the Gallon in Bulk
70% IPA Gallon Case

USP Grade 70%
Isopropyl Alcohol IPA Gallon

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

  1. informative article, thank you. when you wrote “isopropanol is hydroscopic…” did you mean hygroscopic?

  2. Didn’t expect to leave a comment, but this article was very interesting. I was planning to use a 91% solution in a spray bottle to clean out my closet of any mold spores but it seems like diluting it to 70% would be more effective and efficient if I’m reading correctly. Thanks for sharing this useful and practical knowledge!

  3. Sorry, I may have misinterpreted what I read since now I see ISP alcohol does not have effective “sporicidal” attributes as I assumed. Or I may just be confusing myself further lol.

  4. Hi Aaron,

    Isopropyl alcohol is not effective against fungus or 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.

    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.

    Edited for citation updates.

  5. Hi Muhammad. Here is a safety and specification sheet for pure anhydrous 99.8% isopropyl alcohol. You’ll find that it has only one listed ingredient (isopropyl alcohol known by its chemical name as ISOPROPANOL). Other types of isopropyl alcohol that are not anhydrous contain water for dilution such as 70% IPA, or sometimes additives that render it undrinkable. As for checking the purity, the first step would be contacting the manufacturer or checking chemical labels. A non-scientific test for IPA concentration is how fast the alcohol evaporates. 99.8% IPA evaporates very rapidly once exposed to open air, much faster than those mixed with water. Higher concentrations also have a much more pungent smell.

    Does that help answer your question?

  6. Hi Bill, scotch and whiskey do have some favorable antiseptic properties. I think you’ll find this article interesting. The problem is that with such a low volume of alcohol, killing something like gas gangrene and other microbes or bacteria would take up to 18 hours of exposure to the ethanol. “For example, a 50 percent ethanol solution needs 15 minutes to kill E. coli bacteria and 45 minutes to kill strep in a “cooked-meat broth,” but just 20 seconds to wipe out pneumonia and strep bacteria on a glass thermometer — presumably a less hospitable environment. Several common bacteria can be killed off in less than two minutes with 70 percent ethanol, and 35 percent will slay some fungi in a minute flat. The stuff also kills many viruses, including HIV, but at low concentrations the job may take hours.” Note: PAC does not recommend using alcohol products as substitute for proper wound care. Using alcohol for wound care may lead to damaged skin tissue.

  7. Do you have the efficacy data sheet for 70% isopropyl alcohol? Do you know where I can find it?
    I need the list of microorganisms killed by ISP but can’t find it online.
    I would appreciate any help.
    Thank you

  8. Hi, I am looking for Isopropyl Alcohol of less then 10% concentration,where i can get this? I want this to clean the solar Modules.

  9. Hi Anonymous,

    We’ve looked into whether 10% IPA is available from our distributors. It does exist, but is very uncommon in that form, and not something we stock, nor have we seen it anywhere else.

    To answer your question, the simplest solution is to dilute a high purity 99% to 10% IPA concentration with high purity water. Essential you’ll be adding 9 parts water, 1 part IPA. For the best outcomes, and to prevent mineral residues from clouding panels, deionized water is ideal a best practice. (Distilled water still contains ionic content that could cloud finishes)

    Here’s an example of a 91% solution converted to 99%. Just substitute 91% for 10%:

    ———————-

    (Volume IPA) x (IPA current concentration) /(Final IPA concentration) = (Volume Water) /(Final Water Concentration)

    To make 91% IPA from 99% IPA, the problem becomes

    Volume IPA x 0.99/0.91 = Volume Water/0.09

    Choose a volume for either, for example, let’s make a solution with 10mL IPA

    10mL x 0.99/0.91 = volume water/0.09

    Solve for Volume Water= 10mL x 0.99x(0.09/0.91) = 0.98mL

    Take 10mL of your 99% IPA and add 0.98 mL water to get a final concentration of 91% IPA

    ———————-

    I cannot speak precisely to your application, and recommend that you contact the manufacturer for cleaning recommendations.

    If you’re in need of a bulk volume of 10% IPA for a commercial application, give us a call @ 1.888.903.0333. We help businesses source products for unique and uncommon applications everyday.

    99% IPA = https://www.gotopac.com/techspray-1610-g4.html
    Deionized water: https://www.amazon.com/Ecoxall-Deionized-Water-Gallon-jug/dp/B06ZZ75FGT/

  10. Great information. I use IPA to clean surfaces in my home and at work (desk, keyboard, mouse, phone, etc.) So sick of Clorox/Lysol wipes. IPA is inexpensive and effective.

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