Patients and doctors have complained for years about delays in getting appointments for treatment of acne and rashes and routine skin cancer screenings. Now, there is concern that patients can wait weeks to see a dermatologist even for potentially serious problems - with the longest waits in the Boston area.

In a recent study, researchers posing as patients called 851 dermatologists in 12 cities, including Boston, to request an appointment for a 'changing mole' - a possible sign of skin cancer. The average wait was more than a month overall. Boston had the longest average wait - 73 days - though the city had the highest concentration of dermatologists, 4.3 per 100,000 residents.

For certain patients with aggressive skin cancers, doctors say it\'s possible that such a wait could allow the cancer to spread, making treatment more difficult. Measures taken to reduce waits in Eastern Massachusetts, including hiring additional physicians at hospitals and group practices, work only temporarily, some doctors say, and in some cases waits have crept back up.

Physicians say that shortages of doctors in a number of specialties, particularly internal medicine and dermatology, create roadblocks for patients trying to find a new doctor. In dermatology, the waits are created both by patient demand and, some believe, by dermatologists shifting their time to new, more lucrative or complex procedures. Public service campaigns have heightened fear of skin cancer, and melanoma cases are rising, meaning more people are seeking appointments.

At the same time, some dermatologists are devoting time to cosmetic procedures, or to skin cancer surgery that used to be done by general surgeons.