The hair color instructions tell you to always put some of the mixture on the inside of your elbow or some other “discreet” place and wait 24 hours. If no rash develops it’s supposed to safe to use.
I’ve colored my hair many, many times and, I admit, I never do the test. But I also had a terrible allergic reaction to eyebrow waxing last year (something I’d done many times as well, with no prior problems) so it can definitely happen “all of sudden”.
I get my eyebrows ripped at WalMart every few months..
no problem so far..