I'm having an allergic reaction to hair color. my scalp is very itchy. should claritin help? and can i take two 10 milligram tablets?

Unlikely: that claritin would help in this condition, you can try it, but don't exceed recommended dosage, only one tablet of 10 mg You need to see your doctor or a dermatologist, as you may need Rx medications, meanwhile, hydrocortisone cream 1℅ OTC can be applied to the affected areas 2-3 times / day. In the future you want to read the labels carefully and try a small area first, best wishes