Why do alcohol-based disinfectants evaporate so quickly

Alcohol is volatile by nature, which means its molecules escape into the air much more easily than water molecules do. When you wet something with an alcohol-based disinfectant, the alcohol molecules are on the surface exposed to the air, and with ambient heat (which can be pretty intense in summer) they gain enough energy to change from liquid to gas state. The boiling point of ethanol is around 78 degrees, so even at room temperature you've got constant evaporation. Plus, a lot of commercial disinfectants have low water concentration, precisely so the alcohol does its job quickly without leaving everything wet.

That's exactly why they're so useful but also so annoying to use: if you need the disinfectant to work, there has to be contact with the microorganism, but if it evaporates too fast before it takes effect, it loses effectiveness. At home, if you want to disinfect something properly with alcohol, the best thing is to let it act for a few seconds while it's actually wet, not just wipe it on and call it done. It's also important to keep those products with the cap tightly closed, because if you leave the bottle open or half-open, after a while all you've got left is a liquid that's too diluted to be any good.