Why aren't breast implants rejected by the body as something foreign?

Your body will surround the implant with scar tissue. This is called a capsule. This essentially walls off the implant from the rest of your body. Sometimes the capsule can thicken and contract ("capsular contracture"). This is rare, but is a possible risk with breast implants. That said, breast implants are the most studied medical device on the market. I hope this helps! 

Basically because silicone is very nonreactive and sterile.  A sponge has 1 million small holes and fibers for bacteria to cling to, protected, and proliferate your body forms a scar shell around the implant is well sealing it off. Best of luck!
Dr. SubbioBoard-Certified Plastic SurgeonNewtown Square/Philadelphia, PA

Hello,
When people get gauze or instruments left in their body, they only cause a problem when they interfere with normal function of the organs that they are located near, usually due to scaring. Occasionally, they harbor bacteria, which causes infection. They do not however, induce an immune based rejection. Similarly, breast implants do not cause problems either, unless they have excessive scaring or bacterial contamination that leads to infection. They too do not induce an immune based rejection.  The reason implants, instruments, and gauze are not rejected is because they are non-living material. Immune based rejection requires living cells that have identification proteins on their surface that the immune system would recognize as foreign or like. Inanimate objects made of non-living material lack those proteins. Similarly, breast implants have do not induce auto-immune diseases. Don't worry, breast implants are safe. Best of luck!