This is a quote from Don at BWB : "No fridge, fridge equals condensation, condensation equals bacteria".
First, let me qualify that I am not a microbiologist, nor an e-liquid expert by any means, so take this for what it's worth. I'd just like to put this in a little less black and white terms. (I mean no disrespect to Don at all; I realize he has a HUGE following, and clearly knows e-liquid.)
People refrigerate things for preservation. I'm all for that, especially for
storage of e-liquid (at least once it reaches steeping maturity). e-liquid is partly comprised of food grade flavorings. Now, I don't know what happens to them over time, but whatever does, will happen more slowly at a lower temperature.
If you are really worried about bacteria, keep anything you use frequently in, say 10ml, or so bottles outside the fridge, and keep your nic base, and larger quantities in the fridge. When you take them out (to make a new batch or transfer some to a smaller container) just allow them to come to room temperature
before opening them. (Be sure they are mixed well also after they've warmed up!)
From my understanding, nicotine, glycerol, and alcohol (all very common ingredients) all have antimicrobial preservative effects. I could see bacteria being a much bigger problem if water was the primary ingredient in e-liquid but water is generally 0% to 20% (at the very high end) of an e-liquid from what I have read anyway. (I'd venture a guess its most commonly around 5-10%, if it's present at all [instead of PGA]).
Condensation would not generally be good for e-liquid anyway as it will change the formulation if it occurs enough - and PG is hygroscopic (able to absorb water from the environment) to boot. But, I'd think you'd need a lot of condensation to cause the amount of water in an e-liquid to be sufficient to grow bacteria -
in my estimation anyway (again, not an expert here, but this seems sensible to me at least).
If you are keeping small quantities in your fridge that you e.g. refill cartos frequently from just hold them in your hands for a minute or hold them under luke warm water before opening them to at least get them above the dew point.