Oxidation of Nicotine surely will cause a taste issue but the degradation of potency is not a huge problem up until maybe 2 year old juice IMO, and that would be more of a degradation of the flavors before the nicotine. I think some ppl take this oxidation viewpoint to the extreme.
Oxygen Exposure Problems
Exposure to the air has adverse effects on e-liquids of all kinds. Such exposure causes oxidation, a process that begins when air comes in contact with any liquid. The liquids begin to oxidize, which means spoiling and decaying of the e-juice. Although this process generally takes a long period of time to develop, vapers should avoid leaving bottles open for any amount of time unnecessarily. A properly sealed e-liquid bottle or vape cartridge can last well over a year or more, but an opened one should last slightly less than a year in a properly stored environment. Oxidation causes the liquid’s flavor and color to change over time. This is indicated by a darker shade of color in the product tint. There can be a change in odor, but this is less likely to occur in normal storage circumstances.
There are some that think that oxygen exposure causes e-liquid nicotine levels to diminish or drop. There is no evidence to support the idea that oxygen exposure drops or diminishes nicotine content in e-liquids, but overly oxidized products will usually taste bad and should not be used.
So can exposure to oxygen cause nicotine levels in e-liquids to drop? In reality, this isn’t true. Open air exposure causes the flavors to go bad, long before loss of nicotine strength would ever happen. It is exposure to light or high temps that causes nicotine levels to diminish. Even products slightly past their labeled date of expiration should not be harmful or lose their overall potency. Still, the best idea is to always keep your bottles sealed tightly and stored in a cool dark place, but also check their freshness by observing the expiration dates.
It is very common for vapers to become misinformed about products and their usage in the open marketplace. The idea that oxygen exposure causes nicotine levels to drop in e-liquids is one such modern myth, so don’t believe the hype. Do your research will keep your choices well informed as a consumer and self-assured as a buyer, no matter what you are shopping for in the global marketplace.