If you've got both red hair and a fear of the dentist, you're not alone. For years, evidence has shown that the melanocortin 1 receptor gene — which shuts down a protein that would otherwise turn hair brown — also works in the midbrain, where it is thought to lower the pain threshold. That makes it likelier that a redhead who goes to the dentist will need more anesthetic. Other research shows the opposite: that midbrain involvement raises the pain threshold. Both camps agree, however, that hair color and pain sensitivity are linked in some way.