Nicotine
Danger! According to the harmonised classification and labelling (ATP13) approved by the European Union, this substance is fatal if swallowed, is fatal in contact with skin, is fatal if inhaled and is toxic to aquatic life with long lasting effects.
Additionally, the classification provided by companies to ECHA in REACH registrations identifies that this substance causes serious eye damage and causes skin irritation.
Source and more information: https://echa.europa.eu/substance-information/-/substanceinfo/100.000.177