Three sensory systems, olfaction, taste, and somatosensation, are dedicated to the detection of chemicals in the environment. Trigeminal somatosensory neurons enable us to detect a wide range of environmental stimuli, including pressure, temperature, and chemical irritants, within the oral and nasal mucosa. Natural plant-derived irritants have served as powerful pharmacological tools for identifying receptors underlying somatosensation. This is illustrated by the use of capsaicin, menthol, and wasabi to identify the heat-sensitive ion channel TRPV1, the cold-sensitive ion channel TRPM8, and the irritant receptor TRPA1, respectively. In addition to TRP channels, members of the two-pore potassium channel family have also been implicated in trigeminal chemosensation. KCNK18 was recently identified as a target for hydroxy-alpha-sanshool, the tingling and numbing compound produced in Schezuan peppers and other members of the Xanthoxylum genus. The role of these channels in trigeminal thermosensation and pain will be discussed.