I'm willing to go out on a limb and say that a derm resident spends more time in the sun than any neurosuregery resident that gets up at 4 am and leaves the hospital at 8 pm. All the derm resident has to do is simply get to the hospital/office by 7:30 and leaving by 4, which are common hours. Also, tanning might be kinda frowned upon, especially with the deserved melanoma-awareness spiel that they promote in their offices to patients. Point being made is that not all derm residents tan, but that they seem to take care of their aesthetics far more than their colleagues that are residents in other respective fields. This really isn't up for debate.
Bags under the eyes of an ortho resident? Probably due to a 28 hour shift or just standing on their feet and trying to maneuver and hammer some joints around. Bags under the eyes of a dermatologist? Just doesn't fit. Also, keep in mind that derm deals with a lot of patients that pay out of pocket --> these patients are usually well-off financially --> they have no problem with and are probably comfortable around the dermatologist with designer shoes and clothes; the same can't be said for the EM resident working an overnight shift in Detroit.