Pressure ulcers appear in a person who is bed ridden. It is uncommon otherwise. If so than only way to prevent is change the pressure point and take a course of antibiotics if it's infected
Next Steps
If you are not bedridden than I think it could be hair follicular infection which is leaving a scar
Health Tips
Pls donor clear the ulcer with dettol or savlon as though it will clean the germs but will increase the healing time