Use heating pad regularly between legs/ab/thighs. i now have lacy web appearance, very dark, between inner thighs (erythema ab igne?) should i worry?

Heat injury : This is not dangerous but it means you had too much heat exposure. This is a type of heat injury. Some of the changes made may not reverse.

Probably Not: When heat is applied to skin, blood vessels dilate, allowing more blood flow. That's what you're seeing. Unless you begin to have excoriations, breakdown of skin, you should not worry. Now, if you're getting blistered that means damaged skin, so avoid a level of heat that does that. Otherwise, heat is therapeutic.