I mean the juice that contains safe ingredients haha. Thank you for the explanation! I usually buy the juices from big stores over here just to be safe. Maybe I will make my own juices later then (If my country doesn't ban flavours like some states in the US

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safe ingredients are critical. What made ecigarettes work is, except for the batteries, they rely almost entirely on 1950-60s technology. Unprotonated nicotine was heavily researched at a time when public research was done in the US, as were all the other main ingredients. There is a major issue of purity though. Very tiny amounts of other things can cause big problems. In the US there are food safety laws that are relied on very heavily for these purposes. PG and VG are food additives. “USP FOOD GRADE” is an often repeated term here.
Ingredients need to be above 99% pure AND that remaining <1% can’t be dangerous things. The scariest bit is flavorings. Flavorings are made of odd, unusual, and generally proprietary hydrocarbons. Cooking is a chemical reaction. It’s literally chemistry. Application of heat fundamentally changes some things.
There is a testing system for artificial food flavorings in the US though that tests them for baked goods. They are tested up to 450f iirc. It’s not ideal. It’s what we got though. There is also the issue of lipids. Breathing lipids (short chain fats, more or less) does nasty things to ones lungs. Any fat, oil, or wax is made up of lipids, and heating them causes them to recombine into different things. That’s how oil refining works.
The standard guideline is a flavoring needs to pass BOTH the aforementioned test AND contain no lipids. More than a few in the US don’t. An oil based flavoring can still pass the baking tests so they have to be ruled out separately. Also there are loop holes. “Naturally flavored” is a big one. In the US A “natural flavor” gets to skip all control processes because it’s “natural”. This doesn’t actually mean anything because it only refers to “naturally sourced”. If the original donor was a tree who’s sap strongly resembles, say, coal tar, as long as you use that sap instead to create the chemical it’s “natural” even if it’s exactly the same thing chemically as what came out of that coal tar. The coal tar based flavoring has to be safety tested but the “natural” one gets to skip on by. People think naturally flavored things often taste better, and they often do. Not infrequently because the chemicals in that flavor couldn’t pass a safety test if they were artificial, but they don’t have to because they’re “natural”.
People may not trust artificial flavors but it’s the “natural” ones that are potentially more dangerous. Entirely because of that loophole.
Different countries have different systems for this stuff. The EU has systems. I don’t live in the EU so I don’t know how they work but they exist. Your country may as well. They will likely work differently. To use local ingredients you need to know how your local food safety laws work.
Purity of ingredients is a pretty hard safety requirement for ecigs. Lungs are delicate things.