With a BBL, is there a chance for rejection of fat?

There is a very low risk for fat necrosis and infection.  Some surgeons have a much lower rate than others.  Find a BBL expert who
performs hundreds of BBLs each year and has great reviews and great
before and after pictures.Kenneth Hughes, MDLos Angeles, CA

Hello, and thank you for reaching out to us.In my patients, they can expect between 60-80% of the fat to survive. The survival rate depends both on the genetics of your body and the skill of the surgeon. Post surgery, you should follow the plan laid out to you by your surgeon, and avoid putting pressure on your backside (sitting) when possible.Good luck, please let us know how it goes.- Dr. Constantino Mendieta

Since you are using your own fat, your body does not reject it.  Fat is very fragile material, however.  If it does not get adequate blood supply to survive or if it gets crushed, it may liquify and go away (or need to be drained) or harden and even calcify which can lead to palpable lumps.