Bilobol is an alkylresorcinol, a type of phenolic lipids composed of long aliphatic chains and phenolic rings. Chemically, it is similar in structure to urushiol, the irritant found in poison ivy; it is a strong skin irritant itself.
Natural occurrences
Bilobol can be found in Ginkgo biloba fruits.
References
Bilobol Wikipedia(Text) CC BY-SA