These findings, and the observation that intranasal application of acrolein or of the TRPA1 agonist, allyl isothiocyanate, evokes a similar, CGRP-mediated meningeal vasodilatation [47], support the hypothesis that ammonium chloride, chlorine, cigarette smoke, and formaldehyde, all known triggers of migraine or cluster headache [32, 48–51], precipitate pain attacks by their recently identified ability to target neuronal TRPA1 and thereby releasing CGRP [39, 40, 52, 53]. Here, TRPA1 is linked to Cluster headache.