The plant Euphorbia resinifera contains the most potent irritant known so far. It was isolated and identified as resiniferatoxin (RTX).
Resiniferatoxin (RTX) – Potent TRPV1 Agonist for Pain Relief

The plant Euphorbia resinifera contains the most potent irritant known so far. It was isolated and identified as resiniferatoxin (RTX).