Red and sore after brow wax

[Subo]

Hi everyone.
So I have been doing brow waxing about 5 months now. Never had a problem with clients but a few times when iv done my boyfriends his skin has gone red and sore and even scabs over :-/ i keep the heat setting the same for everyone, last night I did a client before him, my self after and we were both fine but my boyfriends are a mess. It doesn't happen every time either. I' baffled. Anyone know what could be causing it?
Thanks

 

[EllenHyuga]

Could he be allergic to it? I did my ex’s middle bit and he erupted! X

 

[Subo]

Could he be allergic to it? I did my ex’s middle bit and he erupted! X

I don' think so because most the time he' fine. Its just been a couple of times it' happened.