What should i major in if i want to become a dermatologist

Actually you do not have a better chance with a bio or chem major. A large number of math and engineers and physics majors get into medical school.
You do not major in medicine. You need to get a Bachelors degree first then apply to medical school, after which you can specialize in dermatology

The first response is absolutely correct. Theoretically you can have major in anything you wish at the undergraduate level, but getting into medical school is very competitive. You will better your chances of admission if you have a degree in one of the basic sciences (Chemistry, biology etc) because admissions counselors will be looking for evidence that you have a good foundation in these.

At the undergrad level, I'd do biology with a minor in ethics or sociology (to show you're well rounded). In graduate school you will major in medicine. Good luck! :-)

For undergraduate, you could do almost anything. Popular choices for pre-med students are biology and chemistry, but I've read that many med schools like it when students major in ethics or liberal art fields.
For graduate school, you will need to go to med school because dermatologists are doctors.