For financial firms, medical areas as diverse as dermatology, physical therapy, primary care, and now even gastroenterology, gynecology and allergy medicine are lucrative targets.

Investment by private equity and venture capital is especially widespread in dermatology, a $14 billion and growing market — and many dermatologists aren’t happy about it. They worry about the effect on patient care, and even fear for the future of their profession if it continues to be dominated by business interests.