It Matters What Medical Alcohol You Use to Disinfect

Stronger is better, right? Concentrated dishwashing detergent degreases better. Stronger rum will get you drunk faster. You even scoop ice cream from the part of the tub where the most fudge and nuts are. But when it comes to medical alcohol, higher concentrations aren’t always better.

Pharmacies usually sell two kinds of rubbing alcohol: a 70% version (for disinfection) and another version at 91% or 99% for… well, that might not be immediately clear. But if you’re going to buy some isopropyl alcohol or ethyl alcohol from a pharmacy, you need to know the difference.

Use 70% When You Need Sanitizer

70% alcohol blends (whether isopropyl or ethyl) are best for disinfection, and if you look at the fine print on the label, they often say that’s what they’re for.

The remaining 30%, by the way, is water. The CDC points out that our best understanding of how alcohol kills germs is that it denatures proteins. Proteins are made up of strands of amino acids, and they can go haywire — essentially unravel and tangle — when we cook them or treat them with certain chemicals. Proteins denature more easily in the presence of water, so the extra water is thought to help the alcohol break down the proteins of viruses, bacteria, and fungi.

Whatever the reason, experiments have shown that the concentration of germ-killing alcohol typically ranges between 50% and 90%, with 70% isopropyl alcohol for rubbing in the middle of the range. 99% of things are not.

Use 99% when you need a solvent

So why do pharmacies sell 99 percent isopropyl alcohol (or even 91 percent)? It’s for cleaning things when you don’t care about killing germs, but when you care about moisture. For example, if you’re trying to make sure electronic components are clean and dry , 99% alcohol is ideal. For the same reason, it is also used to clean the nails of sebum before applying nail polish.

High concentration alcohols are also good as solvents for making some types of paints, inks, etc. For example, I would choose 99% isopropyl alcohol to wipe off marker marks from a dry erase board. Rubbing alcohol is also used as a solvent in this craft , which makes watercolor-style tiles by diluting Sharpie ink. In short, 99% is a great choice for anything medical alcohol can do other than disinfect.


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