Posted by Fred Koenig on Mar 1st 2021

Isopropyl Alcohol - Is 70% Better than 99% Strength?

What is Isopropyl Alcohol (IPA)?

Isopropyl alcohol (2-propanol), also known as isopropanol or IPA, has been used for years as a universal cleaner for everything from hospitals to electronic devices. IPA can be extremely beneficial as a disinfectant when used properly, but there are some disadvantages and even dangerous consequences if it is used improperly. Keep reading to find out why you would need to use isopropyl alcohol and how to use it properly. For further information on the differences in IPA quality, read the article on the importance of high-quality USP IPA. To find out more about the different uses of IPA and why it is important to use the right type of ISP for different cleaning jobs read about ISP as a universal cleaner.

Is 70% IPA better than 99% IPA?

It is important to read the label on your bottle of isopropyl alcohol to ensure it has a concentration of between 60% and 90% alcohol with 10 – 40% purified water. With this formula your ISP will more effectively destroy any bacteria, fungi and viruses. As soon as the alcohol content decreases to below 50% it’s efficacy becomes weakened. Don’t make the mistake of assuming a higher alcohol content means higher quality, the efficacy remains the same if the alcohol content is anywhere between the 60 - 90% mark as long as the purified water is present as well. Isopropyl alcohol concentrations over 91% are not more effective than those between 60% -90%.

Purified water is an essential part of the isopropyl alcohol mixture for the disinfection process. When water is present and combined with isopropyl alcohol, the water acts as a catalyst for destroying or slowing down the growth of pathogenic microorganisms. A 70% IPA solution is able to effectively kill a microbe because it is able to be absorbed through the semipermeable membrane of the cell wall permeating the entire cell, coagulating the proteins and destroying the microorganism. More water content will reduce evaporation, which will increase the amount of time the disinfectant stays on the surface, thereby improving effectiveness to a point. As mentioned previously, isopropyl alcohol concentrations over 91% may become less effective. This is because the higher alcohol content and low water content will cause proteins to coagulate immediately. This causes a protective layer to develop, protecting other proteins from further coagulation.

This is not to suggest that Solutions > 91% IPA do not work at all, they actually will destroy some forms of bacteria eventually. If you are using an extremely high alcohol solution it may take a long time for any bacteria to be killed. Sometimes the spores can lie dormant and later grow active again. In one study, a 50% isopropyl alcohol solution kills Staphylococcus Aureus in less than 10 seconds (pg. 238), but a 90% isopropyl alcohol solution was ineffective even after leaving it to disinfect for two hours. Spores, which are known as chemical sterilants may be destroyed by higher concentrations of isopropyl alcohol solutions. One may wonder why the isopropyl alcohol solutions are so ineffective for bacterial and fungal spores.

You can see more information on the CDC website here .

Can IPA Be Used on Fungus and Fungal Spores?

There is evidence that isopropyl alcohol demonstrates some effectiveness against fungus. Fungal spores are an entirely different matter, isopropyl alcohol will not be able to fight them. Generally, mold and fungus grow in areas of high humidity and moisture. Any surface level cleaner will have a hard time destroying mold and fungus. The most common method of dealing with a mold and fungus problem is to use bleach or hydrogen peroxide. The information about the use of bleach on mold is conflicting.

Government organizations disagree about the use of bleach to get rid of mold, with the EPA not recommending it, and the CDC recommending is as part of mod remediation .

Why is IPA Less Effective Against Bacteria/Fungal Spores?

There are some bacteria that become resistant to alcohol-based cleaners and are able to survive the disinfection process. If some types of bacteria are left in unfavorable external conditions, they may transform into spore cells.

This results in reduced metabolic activity and the ability to survive alcohol-based disinfectants. These spores may lie dormant for any length of time, but when the conditions are favorable again, they may grow active once again. Not all isopropyl alcohol mixtures are created equal. When determining how effective an IPA is one must first consider the intended use, purity, and sterility.

Sterilization vs Disinfection

Proper Uses of Isopropyl Alcohol Require Distinction Between Sanitation, Sterilization, and Disinfection

Disinfection and sterilization have two different meanings and cannot be used as synonyms. These two terms are very often used incorrectly and interchangeably.

The Center for Disease Control (CDC) defines terminology clearly here:

"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."

With this definition in mind, one can see why Isopropyl alcohol is excluded from classification as a high-level disinfectant. ISP does not effectively kill bacterial spores or destroy hydrophilic viruses such as polio. Isopropyl alcohol is, however, widely used for non-critical patient care devices, cleanrooms, pharmaceutics and disinfecting tools in spaces that must be kept perfectly clean.

Surely 91%+ IPA Is Better?

70% isopropyl alcohol is not only useful for use in cleanrooms, hospitals, and medical device manufacturing, it can be used safely for general purpose cleaning as well.

There is little risk of adverse health risks because the odor and toxic fumes emitted are low.

Furthermore, 70% IPA/30% water solutions have less chance of combustion as compared to a higher IPA solution.

When isopropyl alcohol reacts with air, light, and oxygen, it forms unstable peroxides.

This will increase the likelihood of combustion; additional storage time will increase the chance of explosion even more. It is important to be aware of the age of your isopropyl alcohol solution. If it has been stored for over three years it is probably wise not to use it, especially if it has been exposed to air and light over multiple years after opening.

Compared to 99% isopropyl alcohol solutions, 70% IPA is less likely to cause adverse health reactions and is also cheaper for general use and large cleaning jobs. With more water in the solution the disinfectant will evaporate more slowly. This means more powerful cleaning, as the amount of time that the cleaning agent is actually on the surface is extended. With all of these benefits you may wonder why you would ever use 99% concentrations.

Is a Higher Concentration Ever Appropriate?

There are actually several instances where a 99% isopropyl alcohol is a much better choice than a solution with a higher water content.

In any circumstance where the presence of water may cause damage, it is better to disinfect using 99% IPA.

For example, there are several water sensitive devices that would be damaged by the water in 70% IPA These include such things as integrated circuit adapters, computer chips and circuit boards. Any type of worker that requires immediate evaporation and does not want any residue should be using 99% USP IPA to disinfect surfaces.

These jobs include computer technicians, medical device manufacturers, soldering technicians and rework technicians. Rapid evaporation is also ideal when trying to clean sticky residues and grease. In the case of inks and oil clean-up acetone may be your best option.

IPA vs Rubbing Alcohol

Although the terms are often used interchangeably isopropyl alcohol and rubbing alcohol are not the same thing. Rubbing alcohol is not safe for human consumption, as it is a denatured alcohol. It contains an additive that renders it undrinkable. Rubbing alcohol is generally used as a topical antiseptic, but it has many general household uses. Rubbing alcohol contains not less than 68% and not more than 72% of isopropyl alcohol. In documents cited by the CDC, “rubbing alcohol” is defined as 70% isopropyl alcohol and 30% water. The remaining part of the solution may be water, but it may also include perfume oils or color additives.

Types of IPA Explained

Pure IPA

As the name suggests, pure isopropyl alcohol is manufactured and processed without any additives, making it unsafe for human consumption. It is fast evaporating and leaves no residue. Pure isopropyl alcohol is different from sterile or USP-grade isopropyl alcohol.


The United States Pharmacopeial Convention (USP) is a non-profit organization that was founded in 1820. This scientific organization strives to “improve global health through public standards and related programs to help ensure the quality, safety, and benefit of medicines and foods.”

If your cleaner has a USP-grade isopropyl alcohol certification you can be sure that both the isopropyl alcohol and any additives are of the highest quality and the most precise concentration. The USP certification shows that your product has gone through a strict manufacturing, packaging, storage, and inspection process, improving the safety and efficacy of the product for any type of usage.

Sterile IPA

Sterile Isopropyl Alcohol is a solution of isopropyl alcohol that meets the highest standards of purity in aseptic environments. To ensure it's sterile, it's submicron filtered, filled into cleaned containers, double-bagged and gamma-irradiated (usually in a cleanroom). The most common use of this type of alcohol is to completely sanitize cleanroom furniture.

Food-Grade Alcohol

There are few products that use isopropyl alcohol that would be safe for human consumption. You may find isopropyl alcohol in limited food flavorings, fragrances, fats, oils, colorants, preservatives, sweeteners, and probiotics. Ethyl alcohol is generally regarded as safe for food-grade products. The FCC accreditation process provides assurance that a product’s quality is safe for human consumption.

Anhydrous Alcohol

A solution that contains absolutely no water can be referred to as anhydrous. There is really no point in an isopropyl alcohol solution that is completely anhydrous because it will immediately absorb any water out of the air. High quality anhydrous alcohols produce a purity of +99.96%.


Another organization that seeks to protect and improve global health is The National Sanitation Foundation (NSF). The NSF is an independent, non-profit organization. If your product has an NSF stamp of certification you can be assured that it has been tested throughout every phase of the product’s development and has adhered to strict standards. The NSF focuses on a wide variety of areas including food industries, water supplies, consumer products and human environments. In addition to strictly testing and retesting products the NSF performs on-site inspections of the manufacturing plants. If a product or organization fails to meet their standards the NSF may notify the public, recall the product, or possibly de-certify a product.

Industrial-Grade IPA

Industrial grade isopropyl alcohol, is also called technical grade isopropyl alcohol, and it’s most popular use is for non-critical manufacturing and processing tasks. Industrial grade isopropyl alcohol is an inexpensive option for cleaning very large areas. It is useful for removing dirt, debris, grease and adhesives.

Denatured Alcohol

Denatured alcohol is alcohol that contains a chemical that makes it unsafe for human consumption. Denatured alcohol may be used in labs or as an ingredient in certain products such as cosmetics or hand sanitizer. The additive that renders the alcohol denatured may be scented to reduce any odors associated with alcohol vapors. If you see an ad for pure denatured isopropyl alcohol you will know this is misleading as pure isopropyl alcohol does not contain any denaturants.

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