TRPA1 and Headache: For example, hydrogen sulfide (H2S) and nitric oxide (NO) can cause headaches (Benemei and Dussor 2019) and are activated in three ways: (1) cysteine residues of TRPA1 channels are targets of NO, and NO nitrosylation may contribute to channel sensitization (Demartini et al. 2017); (2) when H2S and NO combine to form nitroxyl, the two compounds work together to react with and activate TRPA1 through covalent modification (Benemei and Dussor 2019); and (3) polysulfides (H2Sn) generated from the interaction between H2S and NO also activate TRPA1 (Talavera et al. 2020).