Spike thought about it a bit, laying his curly head on his hand. Seeing as that allergen itself had already been said, he needed something a bit more original. So he thought back to his summer in the woods, and his exploration of the plants there.

"Dock leaves," he said, raising his hand. "They're used to help with the irritation from stinging nettles, because they're meant to contain some kind of anti-histi-something, and I think that's to do with your body not liking the nettle sting." He frowned, annoyed he couldn't complete the word. "And sneezewort, as allergies like hayfever involve lots of sneezing, and if it's been named appropriately it might help.