What causes infections after a BBL?

Infections are very rare, but can happen. They are more common in diabetics and others who may be immunosuppressed. 

BBL infections have never happened in my personal practice experience.  That being said, there are several conditions that exist that may enhance the chance of infection.
1. Smoking slows down healing and increases the chance of other complications including infection.2. Diabetes affects the immune system, and diabetics are more likely to develop post-surgical infections.3. Poorly nutrition before and after surgery affects how a patient will heal and this can increase the chance of infections.
If you are not feeling well and one cheek is much harder than the other, you may have an infection called fat necrosis. 

Infection is rare and rejection of the fat is unheard of since it is your own fatty tissue that is used for the procedure. Fat embolism and pulmonary embolism are extremely rare and I have never seen with several hundred procedures performed. Fat necrosis which appears as lumpy areas can occur, however, the areas will resolve with massage and several weeks of time. Finally, there are normal risks of any surgery such as bruising, swelling and pain.