Read More: Strict New Regulations Are Forcing Vapers to Go DIY

Most e-juices available in stores come infused with nicotine. While this is an optional ingredient when you’re making your own e-juice, for many people vaping is mostly a way to consume nicotine without also sucking down the deadly chemicals found in cigarettes. (It is worth noting that the health effects of vaping are still hotly debated by researchers and that although vaping is almost certainly better than smoking cigarettes, this does not mean it is totally harmless.) It is possible to buy liquid nicotine for DIY e-juice online and in some smoke shops in potencies ranging from a few milligrams per liter to over 100 milligrams per liter. The liquid nicotine will almost always come suspended in some ratio of PG and/or VG.

Freebase nicotine. Image: Daniel Oberhaus/Motherboard

It’s important to reiterate here that nicotine is toxic. Although fatal levels of nicotine consumption is rare in adult humans, a few dozen milligrams is enough to do the job. The lethal threshold is far lower for infants and pets, so make sure to keep the stuff in a safe place. It’s also advisable to wear gloves when handling the nicotine, as it can cause serious skin irritation if it gets on you. In some extreme cases, direct exposure to nicotine can cause symptoms of poisoning, such as dizziness and nausea. I was very careful to make sure I was diluting the nicotine to a level that was less than the ratio that Juul normally uses.

The final ingredient found in almost all commercial e-juices is flavoring. For a DIY e-juice, this can be pretty much any flavor, so long as the flavoring concentrate is water-soluble. Essential oils, for instance, are not a good option for flavoring e-juice both because the oil doesn’t mix well with the PG and VG, and also because some oils have lipids in them that can lead to lipid pneumonia, a type of inflammation caused when lipids enter the lungs.