Like the other 2 above posts said, it is either triggering to you or you have a condition that is making you sensitive to touch. If it's a sensitivity issue, then you might also have sensitivity to light, sound, smells, or tastes. ADD/ADHD and autism disorders are 2 common diagnosis that have sensitivity issue symptoms. I don't particularly like my hair brushed and it's not linked to trauma. When I was a child and my mom still fixed my hair, I'd usually have a meltdown before she was finished. More of autistic symptoms for me. Now my boyfriend wants to massage my head and/or play with my hair, but I'm so sensitive that it irritates me so much. I have alot of other areas that are sensitive other than my head too.