There has been a long-held "debate" among people about 70% Isopropyl Alcohol (PROPAN-2-OL) vs 99%. Even some industry pros consider 99% to be the best method to disinfect their tools and others have argued that 99% is best because it's the strongest. The Centers for Disease Control & Prevention (CDC) did research on disinfecting and sanitizing methods which they published in 2008 as Guideline for Disinfection and Sterilization in Healthcare Facilities. Makeup artist Hillary Wehrle contacted the CDC earlier this year about what do they suggest to clean her cosmetic brushes and products.
Here's the response the CDC sent to Hillary.
"Thank you for contacting the CDC regarding disinfection practices in your practice.So what does this mean? It means that the CDC recommends 70% (up to 91% according to their site) for disinfecting one's tools or even products because 95% and 99% essentially "freezes" (coagulates) the cell. When a cell surface coagulates the best analogy to picture it is Han Solo "frozen" in carbonite. He's alive inside but "frozen" on the outside and nothing can penetrate the shell. Essentially that's what happens to the cell when you use 95% or 99% Isopropyl Alcohol which makes using it for disinfecting purposes useless.
In reference to your first question regarding the recommended concentration for disinfecting surfaces with alcohol, we know that alcohol will denature and coagulate or "fix" proteins. Therefore, alcohol's antimicrobial properties are best used when the alcohol can make contact with key physiological enzymes and protein structure inside a bacterial cell or fungal cell or virus. Use of the more concentrated solutions (95% or 99%) will result in almost immediate coagulation of surface or cell wall proteins and prevent passage of the alcohol into the cell. The benefits of using 70% alcohol are: 1) coagulation of surface proteins proceeds at a slower pace, thereby allowing the alcohol to enter into the cell; 2) 70% alcohol, being a dilution of absolute alcohol, contains water which is essential in the denaturing process of proteins; and 3) because of concentration difference of water and alcohol on either side of the cell wall, 70% alcohol enters the cell to denature both enzymatic and structural proteins. This increases the potency of its antimicrobial properties."
I personally did follow-up with the CDC and specifically asked the following:
Many of my peers swear by 99% alcohol (some use 91%, few use 95%) while I use and advocate the usage of 70% isopropyl alcohol for sanitizing things such as cosmetic brushes and pressed powders or lipsticks. A colleague of mine emailed the CDC and the response is as follows. Is it accurate? Which version should a makeup artist be using to sanitize their work tool and products?Several days passed and eventually a member of the CDC's Division of Healthcare Quality Promotion Public Inquiries team replied to me with the following:
"Thank you for contacting CDC with your recent inquiry as to the most appropriate concentration of alcohol to use for make-up tool sanitation. The information in the previous response is scientifically correct, and explains why the 70% concentration of alcohol has more germ-killing power compared to more concentrated alcohols. When using alcohol to sanitize your make-up tools (or any other device for that matter), you will enhance the overall germ-killing properties of the sanitizing process if you clean your tools and brushes first and rinse them very well with water. The cleaning step will help to physically remove skin cells and make-up chemicals from the tools and brushes, thereby minimizing the amount of soil and protein material that can reduce the potency of the alcohol. To further enhance the sanitizing effect of the alcohol soaking, allow the tools and brushes to soak for a few minutes, then rinse with clean water and allow to dry."
So which % of Isopropyl Alcohol should a makeup artist or even you should be using to sanitize and disinfect their products or tools like brushes? 70% to 91% per the CDC. Save the 99% for alcohol activated cosmetic palettes because alcohol palettes such as PPI and other types use 99%. Can't find anything less than 99% or 95%? You can dilute it down using distilled water but you need to make sure your ratios are accurate or it may not be effective. I use 70% and 91% (I like the Trigger spray in my 91% CVS bottle) when sanitizing my tools.
Big thanks to Hillary Wehrle for contacting the CDC and getting clarification on which % to use!