I read a white paper a couple of days ago that talks about the scarcity of any recent studies on the toxicity of nicotine, and in fact they claim it's probable the (ballpark figure) 40 to 60 mg toxicity level being quoted today in medical journals may actually be "sourced" from self-research done by doctors in the late 1800's. They gave themselves nicotine, documented what the results of their tests were, and predicted how much more nicotine they would have to give themselves before it killed them, wrote that figure down and then that figure became the official "this much nicotine will kill a person" figure. It's a secondary avenue for me right now. At this point I've got about 20 links that I need to research in order to get up to speed on vaping, etc... and haven't the time to chase this one down, but this is definitely a question that needs a high quality answer.
Based on some articles here, the real number is thought to be somewhere between 500mg and 1000mg OR HIGHER. No one seems to know the basis of that LD50 number. This article says probably 20x that 60mg LD50 number...
Nicotine Propaganda
I think I would have to use it as a skin care treatment (100mg concentrate) to even start having serious problems, but that is just my guess as to the "skin contact toxicity" issue. If you put a couple ml of VG or PG on the palm of your hand, what happens? Does it get sucked right in? No, it sits there

. I don't think anything changes if it has up to 10% nicotine in it (100mg) and in fact I mentioned I already tested that on myself.
I'd have to drink it to really have a problem, I can't think of any other way to have a problem. But the problem with this is that I've seen a number of 10x in terms of variances in nic tolerance from person to person and maybe I'm on the high side, maybe I'm off he charts (in theory in principle...who knows?).
So I just came to the conclusion that people are generally way overly cautious when talking about it. Which is good, in that no one ever got hurt being overly cautious handling chemicals. OTOH a lot of people are afraid to do DIY, even with 24mg nic that they could vape straight up, without any effect worse than a headache or nausea if they are low tolerance 3mg users.
Most people have trouble threading needles like this... it's just the way it is.
if I had children, or my cats paid more attention to my juice components, then I would be far more cautious because dose makes the poison, and body weight determines that dose.
I really think politics has a lot to do with this. Certain people like the current LD50 number because they want nic to appear scary and toxic and bad for you... so they can tax it.
This is an interesting read....
Caffeine Overdose Symptoms: Signs, Cases, Prevention
According to that, many people have OD'd on caffeine, some fatally. Note the specific case studies. Of course, you never hear much about that. I'm not sure anyone has managed to fatally OD on DIY nic yet*, and if it happened it would be headline news for a month. That's politics and propaganda.
* In a documented case, not some media blip that was never well substantiated.