All kinds of stuff might cause burning. I've heard some wacky things about AA's gear - though I've used their MENT without issue. Some things that are normally used might be guiacol, too much benzyl alcohol, or doofuses that clean their glass with isopropyl alcohol (or bleach) and leave residual in the mix. All of these things though you would most likely feel the burning immediately.
Things that might have made their way into the brew... god only knows. Maybe a bottle of Comet cleanser fell over on the desk that day. Your guess is as good as mine. Either way... if you're not getting rubbing alcohol in your site, gear should not burn. Red flag.