Most contain nicotine, however, you can get nicotine-free Elf Bars as well.
The Elf Bar 600 (the most popular range of Elf Bars), contains 2% nicotine strength nic salt e-liquid. 2%, or 20mg/ml, is the highest strength nicotine e-liquid allowed on the UK market today and offers a strong hit to counter nicotine cravings.
Nicotine salt e-liquids are a different composition of nicotine compared to freebase nicotine. They both come from the tobacco plant, but nicotine salts are processed to create the purest form of nicotine possible. This means that smaller quantities are needed to provide the same kind of nicotine rush as with freebase nicotine (which is the kind of nicotine you get in tobacco cigarettes and other types of e-liquid). Nicotine salts are also more easily absorbed by the body than freebase nicotine, resulting in a smoother throat hit.
However, there are some ranges of Elf Bar that have lower levels of nicotine or 0% nicotine.