Do silicone buttock implants only cause illness if they leak?

The "illness" or "autoimmune disease" you question is regarding silicone gel breast, not buttock, implants. After vigorous and intense research across the globe it was found that even silicone gel breast implants do not cause cancer or autoimmune diseases. Nonetheless, silicone gel buttock implants are not FDA approved and thus not legal for buttock implantation in the USA. I actually see about one patient a month that had gel implants done in another country and, although they looked a felt great at first, they are now seeking revision because the implants are either visible on top of the muscle and/or grossly deformed by scar contracture or a ruptured implant. The soft semi-solid silicone rubber implants used in the USA are much less likely to have these problems if placed correctly under the gluteus muscle AND are considered permanent implants because they cannot rupture and leak silicone gel.  Breast implants can rupture and leak thus replacement every ten years is the general recommendation. Similar to breast implants, as long as the appropriate implant size/shape is selected and the implant is placed in the correct anatomic plane (i.e. either under or within the gluteus maximus muscle but not on top of or "subfascial"), the end result should  look and feel natural - like an athletically fit buttock. Glad to be of help .

Buttock implants (used in the US) are made of a soft solid silicone and cannot leak.  Breast implants are made of a silicone gel which can occasionally leak. Extensive scientific studies of silicone breast implants showed that they had no relationship to autoimmune or other diseases even if the implant leaks.  The silicone breast implants are the single most-studied medical device in the history of the FDA and were found to be perfectly safe.  There can be complications with any implant such as infection, malposition, capsular contrature, etc., but the implants themselves do not cause any illnesses.