Further it may have NOTHING whatsoever to do with the synthetic hair compounds but rather irritation from the materials used in the base of the wig itself - such as the stretchy mesh they use in the wig base or the straps or some other element other than the synthetic hair itself.  You could TRY a human hair wig, and if the problem then still persists, then you'll know it's not the synthetic hair but rather the wig base cap to begin with.  I DO however, agree wholeheartedly with EVE with this business of people not WANTING to wear wigs - men or women - just to get out of that by faking or attesting to allergies.  I think for the most part it's bogus. I'm not saying people don't have allergies. EVEN I have allergies. But you know what, most of the time, I totally ignore them and I think in doing so, for me, they never become quite the issue that someone who pampers an allergy has to deal with.  I am not diminishing their conditions by saying so in any way.  I don't mean to do that.  I think it's a matter of being a bit of a whiner - I've seen that EVERY TIME someone has to wear a wig onstage. Personally I love it. Sure they make me itch a little bit but I can survive it if it helps the look, the intent of the author and moves the show along as it is intended to do.  AND when it calls for it, and as EVE said, if they KNEW what it would involve and didn't say anything at the outset, that's their fault.  Crazy stuff.  And again someone else said it - try a cotton cap if possible.  Keep the latex away from them.  Maybe it's latex that 's a problem.  Latex in elastic in the wig base or something else.  Sounds like a way to not have to wear the wigs though if you ask me.  And maybe that's unfair if this person truly does have significant allergic issues.  But otherwise, I guess you're stuck with an actor who CAN'T wear a wig. What does that mean for your next move when the show CALLS for it?  Hard to say.  GOOD LUCK.  Oh yes, and there ARE injections and pills their doctor can prescribe to alleviate any problems that come from the exposure to those things to which they're allergic so THAT should be considered as a means to get past their problem. Like...duh!! I wonder why THEY didn't think of that one.  Tell you why!! They don't WANT to wear the wigs.

Oh by the way, you may be able to try a barrier cream of some sort on their skin too  in order to aid a little bit in protecting them from being bothered by it.  Tough spot with only three weeks left to go.  Just for the fun of it, and if the show actually DEMANDS that the lead actor wear a wig and it's integral to the show, tell them that you'll just have to replace them and watch to see if they "give in" and become the martyr and wear the wigs "being the trooper they are"!! THAT would be an interesting test.  I'm so bad.  I'll shut up now.