70% vs 91% vs 99% Isopropyl Alcohol: Which One to Use
Published by Harmony Lab & Safety Supplies on Nov 03, 2026
Published November 2026
- Disinfecting skin, tools and surfaces: use 70%. The CDC says alcohol kills germs best at 60–90% in water. The water helps it work, and it slows evaporation so the alcohol stays wet long enough.
- Electronics, optics and residue removal: use 91% or 99%. Less water means faster drying and less moisture left behind.
Why 70% Usually Beats 99% for Killing Germs
The CDC's disinfection guideline puts the most effective concentration at "60%–90% solutions in water." It also notes that pure alcohol is less effective than alcohol mixed with water. Alcohol kills bacteria and many viruses, but it does not destroy bacterial spores. It also evaporates fast, so a surface has to stay visibly wet to be disinfected (CDC).
70% vs 91% vs 99% Isopropyl Alcohol Compared
| Strength | Best for | Dries | Products |
|---|---|---|---|
| 70% | Disinfecting skin before injections, small surfaces, thermometers and tools; cleanroom wipe-down | Slower; stays wet longer | Read Right SurfaceKleen 70% wipes, Medline 70% IPA, TekniSat 70% IPA presaturated cleanroom wipes |
| 91% | General cleaning of electronics and equipment, removing adhesive and flux residue | Faster | CleanTex 91% alcohol wipes, Medline 91% IPA |
| 99% and up | Circuit boards, card readers, optics and connectors, anywhere water is a problem | Fastest | CleanTex 99% IPA, 99.7% electronics cleaning wipes, 99.9% IPA foam snap swabs |
Bottles, Wipes or Presaturated Wipes?
- Bottles: best value for large areas, or for filling a dispenser or spray bottle.
- Presaturated wipes: every wipe has the same alcohol content, there's no spill risk, and they're quick to use at the point of work. See alcohol wipes.
- Cleanroom presaturated wipes: low-lint polyester or polypropylene wipes pre-wetted with IPA and packed in cleanroom-grade bags. See presaturated wipes.
Safety
- Alcohol is flammable. The CDC advises storing it "in a cool, well-ventilated area." Keep it away from sparks and heat, and let surfaces dry before powering equipment on.
- Test a small spot first on plastics, coatings and screens. Some finishes don't tolerate alcohol.
- Wear nitrile gloves for frequent use. IPA dries out skin.
Frequently Asked Questions
Can I use 99% isopropyl alcohol to disinfect?
It works, but it's less effective than 70% and evaporates before it has time to work. Use 70% for disinfecting.
Is 91% isopropyl alcohol a disinfectant?
91% is just above the CDC's 60–90% range. For disinfecting, 70% is the safer choice.
What is 99% isopropyl alcohol used for?
Cleaning electronics, optics and connectors, and removing residue where water would cause problems.
Can I dilute 99% IPA to 70%?
Yes. Mix about 7 parts 99% IPA with 3 parts distilled or deionized water.
Source: CDC, Guideline for Disinfection and Sterilization in Healthcare Facilities, Chemical Disinfectants (Alcohol). See also Isopropyl Alcohol vs Ethyl Alcohol.