Breast implants are silicone rubber shells filled with either saline (sterile saltwater) or silicone gel, surgically placed beneath breast tissue to increase volume and change shape. They work by creating a pocket inside the chest, where the implant sits and the body gradually forms a natural tissue lining around it. The device itself is relatively simple, but the way your body responds to it, and the choices made during surgery, determine the final look and feel.
What’s Inside the Implant
Every breast implant starts with the same basic structure: an outer shell made of silicone rubber (silicone elastomer). What differs is the filling. Saline implants contain sterile saltwater. Silicone implants contain a silicone gel that mimics the density and movement of natural breast tissue more closely than saline.
Within silicone implants, there’s a spectrum of gel consistency. Standard silicone gel is somewhat fluid, while “cohesive” gel implants (sometimes called gummy bear implants) use silicone molecules that are tightly cross-linked together. If you cut one in half, the gel holds its shape rather than flowing out. This matters most in the event of a shell rupture: cohesive gel stays in place instead of migrating into surrounding tissue. The tradeoff is that gummy bear implants require a larger incision during surgery because they can’t be compressed as much going in.
Saline implants have a distinct mechanical advantage during placement. Because they have a fill valve built into the shell, the surgeon inserts them empty and then fills them with saline once they’re positioned inside the body. This allows for a smaller incision and lets the surgeon make fine volume adjustments during the procedure. Some models even have a valve that allows saline to be added or removed after surgery for further fine-tuning.
How the Body Responds
Once an implant is placed, your immune system recognizes it as a foreign object and launches what’s called a foreign body reaction. This isn’t a sign of something going wrong. It’s a normal, predictable process that mirrors wound healing, and it’s actually what holds the implant securely in place long-term.
In the first phase, blood proteins coat the implant surface and signal immune cells to investigate. Inflammatory cells arrive and attempt to break down the foreign material. When they can’t (the implant is far too large and chemically inert to digest), the body shifts strategies. Instead of fighting the implant, it walls it off. Anti-inflammatory signals take over, calming the initial response and directing the construction of a tissue barrier.
Over the following weeks and months, specialized cells called fibroblasts lay down collagen fibers around the implant, forming a thin, flexible envelope known as the fibrous capsule. Early on, this capsule is soft and vascular, composed of immature collagen. As it matures, it becomes denser and stronger, eventually settling into a stable lining of mature collagen. In most people, this capsule stays thin and pliable, and you never notice it. It essentially becomes the implant’s biological pocket.
When the Capsule Becomes a Problem
In some cases, the capsule thickens and tightens excessively, a complication called capsular contracture. The implant gets squeezed, which can make the breast feel firm or hard, change its shape, or cause discomfort. This can happen with any implant type and in any placement position, though the underlying triggers differ depending on the surgical approach. Bacterial contamination (biofilm forming on the implant surface) is one suspected driver, and textured implants may be slightly more prone to harboring bacteria than smooth ones.
Placement: Over or Under the Muscle
Where the surgeon positions the implant relative to your chest muscle significantly affects how it looks and behaves over time. There are two primary options.
Subglandular placement puts the implant between the breast tissue and the chest muscle. Recovery tends to be less painful because the muscle isn’t disturbed, and the implant doesn’t shift when you flex your chest. The downsides: the implant edges can be more visible or palpable (especially in thinner patients), and rippling along the surface is more noticeable because there’s less tissue covering the device.
Subpectoral (under the muscle) placement tucks the implant beneath the pectoralis muscle, at least partially. This adds an extra layer of tissue over the upper portion of the implant, which reduces visible rippling along the top of the breast. But the muscle introduces its own complications. Flexing the chest can temporarily distort the breast shape, and one long-term study found a 94% rate of upward implant migration at seven-year follow-up after initially correct placement. Muscle strength plays a direct role: the stronger the muscle, the more it can push the implant out of position over time.
Smooth vs. Textured Shells
Both saline and silicone implants come with either a smooth or textured outer surface, and this affects how the implant interacts with the surrounding capsule. Textured shells are designed to grip the surrounding tissue, which helps prevent the implant from rotating or shifting position. This is particularly important for shaped (teardrop) implants, where rotation would be noticeable. Smooth implants move more freely within the pocket, which is usually fine for round implants since they look the same regardless of orientation.
Textured implants have been associated with lower rates of capsular contracture and malposition, but they carry a higher rate of certain infections due to bacteria adhering more readily to the rougher surface.
How They’re Placed During Surgery
Surgeons access the chest through one of several incision points. The most common in the United States is the inframammary incision, a cut along the natural crease beneath the breast. This gives the surgeon the widest access and best visualization, making it the preferred route for silicone implants in particular.
The periareolar incision runs along the lower edge of the areola, where the scar blends with the natural color transition. It works well when combined with a breast lift and is a good option for people prone to thick, raised scarring in other locations. Two less common approaches, through the armpit (transaxillary) and through the navel (TUBA), are only possible with saline implants because the empty shell can be threaded through a narrow tunnel and filled once it’s in place.
How Long Implants Last
Breast implants are not lifetime devices. Based on large-scale data on the latest generation of implants, the average lifespan (defined as the time between insertion and rupture or removal) is roughly 9 to 10 years. For modern silicone implants, rupture-free survival is about 98% at five years and 83% to 85% at ten years. That means roughly 15 to 17 out of every 100 implants will develop some form of shell failure within a decade.
If a saline implant ruptures, you’ll know quickly: the saltwater leaks out and is harmlessly absorbed by your body, but the breast visibly deflates. Silicone ruptures are harder to detect because the gel (especially cohesive gel) tends to stay in place even after the shell breaks. These are called silent ruptures, and they often produce no symptoms at all. Imaging, typically an MRI or ultrasound, is needed to identify them.
Reoperation rates are substantial even beyond rupture. FDA post-approval studies found that 20 to 40 percent of augmentation patients and 40 to 70 percent of reconstruction patients required additional surgery within the first 8 to 10 years for reasons including contracture, malposition, asymmetry, and pain. Because implants will likely need replacement multiple times, estimates suggest a person who gets implants at a young age may undergo roughly five replacements over a lifetime.
What Determines the Final Result
The implant itself is only one variable. The final appearance depends on the interplay between implant size and shape, the placement depth (over or under the muscle), shell texture, the incision approach, and your body’s own tissue characteristics. A person with more natural breast tissue will have better coverage over the implant, less visible rippling, and a more natural contour regardless of which implant type they choose. Someone with very little breast tissue will see more of the implant’s edges and may benefit more from under-the-muscle placement for additional coverage.
Over time, gravity, aging, weight changes, and the ongoing biological interaction between your tissue and the implant all continue to shape the result. The capsule can thicken. The implant can shift. The breast tissue around it can thin. These are the reasons implants require long-term monitoring and, eventually, replacement or removal rather than a single surgery that lasts forever.