A sternutatory is a substance that induces sneezing. The word is also an adjective: if you want to be grand about it, you can refer to sneezing as the sternutatory reflex or as sternutation. Both words come from Latin sternuere, to sneeze.
Sternutation appeared first in English in 1545, in a medical work on midwifery, The Byrth of Mankynde, Otherwyse Called the Womans Booke; it referred to infants troubled with “sternutation and sneesynge”. Sternutatory often turned up in old herbals, here about the herb mountain arnica:
Its principal use at present is as a sternutatory. The root is perhaps the strongest of all the vegetable errhines, white hellebore itself not excepted.” Sternutatories were believed to help expel noxious influences from the body.
The Botanist’s Companion, by William Salisbury, 1816. (Errhine, now even rarer than sternutatory, had much the same meaning. It comes via Latin from two Greek words meaning “in the nostril”. The same root appears in rhinitis, inflammation of the mucous membranes of the nose, and in rhinoceros, literally the animal with a horn on its nose.)
Writers outside the medical field found sternutatory to be usefully humorous, if somewhat ponderous. This is from Sea and Shore of 1876, by the Kentucky writer Catharine Warfield:
“Good snuff is not to be sneezed at,” said Major Favraud. “None offered to young ladies, it seems,” taking a huge pinch, and thrusting it bravely up his nostrils, as one takes a spoonful of unpleasant medicine. Then contradicting his own assertion immediately afterward, he succeeded in expelling most of it in a series of violent sternutatory spasms, which left him breathless, red-faced, and watery-eyed, with a handkerchief much begrimed.
The word can be found in some modern dictionaries because the term was taken over in the early twentieth century to describe an agent used in chemical warfare that causes irritation to the nose and eyes, pain in the chest, and nausea.