Why can e-juice become darker after the bottle has been opened?

E-juice is a liquid intended for compatible refillable e-cigarettes. The product is also called vape juice, e-liquid or e‑liquid. It typically consists of propylene glycol (PG), vegetable glycerin (VG) and flavorings. Depending on the product it may contain nicotine or be nicotine‑free.

E-juice is available in several formats:

- 10 ml e-juice is a ready-to-use e-liquid in smaller bottles and can be available with or without nicotine.
- Nicotine salt contains nicotine in salt form.
- Shortfill is nicotine-free e-juice in a larger bottle with free space.
- Longfill contains flavor concentrate in a larger bottle and is not a ready-to-use e-liquid.

Check the product information for content, volume and nicotine strength.

The product's nicotine content is stated on the product page and packaging, usually in milligrams per milliliter, mg/ml. A product listed as 0 mg/ml is nicotine-free. Always check the current product information as nicotine content and nicotine type vary between different e-juices.

VG stands for vegetable glycerin and PG for propylene glycol. The ratio is usually given as, for example, 50/50 or 70/30 and affects, among other things, the liquid's viscosity. Which VG/PG ratio is compatible depends on the e-cigarette's construction, pod, tank and coil.