Reapers pull in around 1,500,000 to 2,200,000 SHU
Then there is Pepper X which is 2,693,000 SHU.
After that extracts which range all the way up to pure capsaicin which is 16,000,000 SHU.
Nothing can be hotter then that. People claim hotter by saying you can stack two 10m extracts etc but that's just volume not technically hotter.
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Update I pulled out 4th my stomach couldn't handle it. Got the biggest cramps so I'm lying on my bed suffering at the moment waiting for the cramps to pass
At 16 billion Scoville units, resiniferatoxin is rather toxic and can inflict chemical burns in minute quantities.
For rats, LD50 through oral ingestion is 148.1 mg/kg. It causes severe burning pain in sub-microgram (less than 1/1,000,000th of a gram) quantities when ingested orally.
Though since it is so potent, it sounds like you can still taste it well below the toxic concentration.
Disclaimer: I am not a doctor or food science expert, and cannot endorse tasting random chemicals with the word "toxin" in their name.