"Yes, but it's supposed to revitalize your skin" Strange thinks. That seems to be a general theme of these baths: soak in this, it'll absorb through the skin, that'll revive you. Though, come to think of it, Syrlya doesn't actually have skin.

"I'm certain that it'll work the same with your leafy bits," Strange says, with a slightly dismissive hand gesture. Right? Right! They'd have stopped Syrlya if this was toxic to plants or something like that (he thinks), time for Syrlya to get a revitalizing treatment as well.