What Causes Patches Of White Skin In Groin Area?

I am a healthy, active 72 year old woman. Just had a physical. My doctor suggested seeing a dermatologist for a circle of thin white skin on the inside of both legs in my groin where the skin is normally darker.

What are the implications?

Height 5ft 5in, weight 192--counting calories to lose weight. Normal blood pressure, some arthritis.