To be a dermatologist, you have to go to medical school. Very few, if any, schools would offer an undergraduate major in dermatology. You would have to choose a major (many pre-med students choose biology or another life science) and then take pre-med courses to apply to medical school. It seems like Loyola Chicago has a pre-health (equivalent to pre-med) program. Check out details here: http://luc.edu/prehealth/.