Are there any types of face scars that dermabrasion is bad for?

Active or atrophic: Active acne lesions with infection or atrophic scars with minimal or absent epithelium are not good scars for dermabrasion.

Usually not: The most difficult scarring for any treatment is the deep "ice-pick" types scars. Dermabrasion is effective on improving most other irregular or uneven scars. It should not be used for immature, hyperactive or excessive scars (like keloids).

Infected scars: Dermabrasion should not be done on infecteds scars (espeically cystic acne that is still infected) or on patients of color.

Yes: Hypertrophic or keloid scars may not be improved by dermabrasion. They may, in fact, be worsened.