When to skip pcp visit and go straight to a dermatologist?

It depends. If you have a skin issue your PCP has not been able to help with, self referral may be reasonable. Some health plans will not cover self referrals, requiring a PCP seek pre-authorization after an office visit. If your coverage allows self referral, do as you wish, but specialty visits often have a higher co-pay to discourage visits when your PCP could do the work.

In 2 circumstances where I'd go directly to a dermatologist is if you have a skin lesion that stands out as very different from other skin spots on your body and if a chronic skin lesion shows enlargement or other change. I've seen too many malignant melonomas that have been misdiagnosed by MD's and even a few that were missed by dermatologists.