From a chemistry perspective, there are several types of alcohol, but the one of interest here is the alcohol you can drink, which is ethyl alcohol or ethanol. Technically, none of the types of alcohol go bad or expire in pure form or when diluted with water. Alcohol is a potent disinfectant, so when it is present in a high enough concentration, it's safe from mold, fungi, protozoa, and bacteria. It's only when alcohol is mixed with other ingredients that it has a shelf life.
Why Is 70% Isopropyl Alcohol(IPA) a Better Disinfectant Than 99% Isopropanol, And What Is IPA Used For?
IS SODIUM HYDROXIDE SAFE IN BEAUTY PRODUCTS?