How to tell if e-liquid has gone bad: 24 months of data
How to tell if e-liquid has gone bad, sign by sign: what a 24-month aging study measured for colour, flavour and acidity, and what it never tested.
To tell if e-liquid has gone bad, look for a liquid much darker than when new, a flavour gone flat, and any harsh off note. A 24-month aging study backs the first two: most flavoured liquids darkened and most flavourings lost at least half their concentration within two years in ambient light. It did not measure smell or taste.
The study is by a Roswell Park Comprehensive Cancer Center team, published in ACS Omega in 2025; this desk read its full text on 23 September 2026. The three retailer checklists read for this piece cite no study of what breaks down, or when.
One caution before the signs. The subjects were 20 lab solutions, each a single flavouring in 55:45 PG/VG with 40 mg/mL nicotine, plus 14 MyBlu liquids bought in November 2019. Not every bottle on your shelf.
How to tell if e-liquid has gone bad, sign by sign
| Sign | Measured? | What the study found |
|---|---|---|
| Darker colour | Yes | Most lab liquids and all 14 MyBlu liquids darkened in ambient light; less in cold dark |
| Flavour fade | Yes | Half lost by 6 / 24 months: 11 / 16 of 20 in ambient light, 6 / 10 in ambient dark |
| More acidic | Yes | All 20 lab liquids more so in ambient light than in the dark; MyBlu average pH 5.7 at start, 4.3 after 24 months in ambient light |
| Smell, taste, thickness | No | Not measured |
Colour is the sign you can check without opening the cap, and the study’s controls point at nicotine: the nicotine-only control darkened, the plain solvent never did. Our dark-brown post has the oxidation story.
What does bad vape juice taste like?
Thinner, is the honest answer, because the loss the study measured was flavouring concentration. The fastest to go were cinnamaldehyde, ethyl and methyl salicylate, furaneol, limonene and triacetin. A bottle that tastes of less than it did fits that loss, though nobody in the study tasted anything. Cold dark storage lost least, and our fridge post makes that case. The study tracked flavourings, not nicotine; our salt-vs-freebase post covers nicotine retention.
Is there a change you cannot see?
Acidity. Every lab liquid kept in ambient light ended more acidic than those kept dark, and the MyBlu average fell from pH 5.7 to 4.3 there.
How to tell if e-liquid has gone bad: reader questions
Can you vape expired e-liquid?
The study cannot answer that as a safety question. Aerosol from four aged lab solutions, ethyl maltol, furaneol, maltol and triacetin, showed no significant cytotoxicity difference from fresh in one cell test. That covers four single-flavouring mixes, not your bottle, and it is not a finding that expired liquid is safe.
Does e-liquid go bad?
Its flavourings do. In the study, 16 of 20 lost at least half their concentration within 24 months at room temperature in ambient light, and all 20 ended more acidic there than in the dark. The authors wrote that the expiry dates some makers print are not based on federally mandated US standards, and back labelled dates built on stability testing.
Why has my e-liquid turned brown?
Mostly nicotine and light, on this evidence. The nicotine-only control darkened in the same pattern as the flavoured liquids, while the plain PG/VG solvent control never darkened in any condition. Darkening was strongest in ambient light and weaker in the cold dark arm, furaneol excepted.
The sober point, as ever. A fresh bottle tastes better than a stale one; it is not a healthier one, and nothing here says otherwise. Nicotine is an addictive chemical, and this site is for adults of legal purchase age only.