Two sessions ago, during our weekly Pathfinder game, my bard almost kicked the bucket. She got saved in time by the other players, but it was really close. So afterward, our (LN) inquisitor approached her and discreetly handed her a wand of 'Infernal Healing' with the instructions to use it next time, please.
Now, Infernal Healing has the [evil] descriptor and fluff-wise I always took it as some sort of subtle temptation. Yeah, it's useful, but it still works with devils blood/unholy water and you are kinda dealing with evil. Accepting help from devils – slippery slope and all. The bard recognized the spell, but is not worldly/wise enough to know what to expect from it.
I heard that using spells with the [evil] descriptor shift your alignment to neutral after 3 uses and then it's two more uses till you're evil. Further research turned up conflicting information. Soooo… is this true in Pathfinder? Does it apply to wands as well? And is this a slightly magical/mind-controlly thing or just mundane 'your PC is doing evil stuff, so they're evil now'?
Admittedly, it would be pretty funny if the CG (“nicest member of the party”, according to the inquisitor) bard slowly got corrupted with nobody noticing… the staff still has 40+ uses, after all….
Best Answer
According to the most recent rulebook on this topic, you are correct that casting evil spells corrupts your character's alignment.
The most recent main Paizo RPG line book that discussed this subject was Horror Adventures, which had this to say about casting spells that are aligned (page 110):
This is where the "two evil spell castings turns you neutral and three turns you evil" guidance comes from. Note that it adds in all sorts of qualifiers: if there's a big delay between castings its less of a big deal, if you do it with good intentions it has less impact on your alignment, etc.
But maybe its better to not follow this one...
This rule has been seen as highly contentious by the Paizo forum community as it opens big and thorny questions like: "Can every evil npc simply use 2 uses of a wand of protection from evil on themselves to change their alignment to neutral temporarily and remove their vulnerability to the paladin's smite evil?" and similar problems.
While the context provided (core line rules book, no "optional rule" language) suggests that this is a base-line update to how aligned spellcasting works, your GM has the freedom to use or ignore this change as they'd like (and I think the forum consensus is that its best to ignore it :>)