Breast expanders are temporary, balloon-like implants placed under the skin or chest muscle to gradually stretch tissue and create space for a permanent breast implant. They are most commonly used after mastectomy, giving the body time to grow enough soft tissue to support a natural-looking reconstruction. The process typically involves two surgeries: one to place the expander and a second, months later, to swap it for a permanent implant.
How Expanders Work
A breast expander has a silicone shell, similar to a breast implant, but it starts mostly empty. Built into or attached to the shell is a small fill port. Over the weeks following surgery, your surgeon injects saline (sterile salt water) through this port using a needle, gradually inflating the expander. Each fill session stretches the surrounding skin and muscle a little more, much like how pregnancy stretches abdominal skin over time.
Filling typically begins 7 to 14 days after the initial surgery. From there, you return to your surgeon’s office every one to two weeks for additional saline. The entire expansion phase usually takes two to three months, though it can be shorter or longer depending on how much volume you need and how your tissue responds.
Who Gets a Breast Expander
The most common reason is breast reconstruction after mastectomy. When a mastectomy removes breast tissue, the remaining skin and muscle are often too tight to accommodate a full-sized implant right away. An expander solves this by slowly building that space. Beyond cancer reconstruction, expanders are also used to treat underdeveloped breasts, correct soft tissue deformities, and address combined chest wall and breast irregularities.
Where the Expander Sits in the Body
Surgeons place expanders in one of two positions: under the chest muscle (subpectoral) or on top of it, just beneath the skin (prepectoral). For years, subpectoral placement was the standard approach, with the expander tucked beneath the pectoralis major muscle for added tissue coverage. It works well, but it comes with trade-offs. Manipulating the chest muscle causes more postoperative pain, can weaken the muscle, and frequently leads to “animation deformity,” where the breast visibly shifts when you flex your chest. That happens in more than 70% of subpectoral cases.
Prepectoral placement avoids all of that by leaving the chest muscle untouched. Pain scores are lower, animation deformity is essentially eliminated, and recovery tends to be easier. To make up for the thinner tissue coverage, surgeons wrap the expander in a biological support material called acellular dermal matrix, a processed tissue graft that acts like an internal sling. This material helps hold the expander in the right position, supports the lower part of the breast, and allows for more controlled expansion. It also appears to reduce the long-term risk of capsular contracture, the hardening of scar tissue around an implant, from roughly 8 to 17% down to about 3%.
The Exchange Surgery
Once the expander reaches the target volume and the tissue has had time to recover and reestablish blood supply, a second surgery replaces the expander with a permanent breast implant. This is a shorter, less involved procedure than the initial placement. Your surgeon removes the expander, adjusts the tissue pocket if needed, and inserts a silicone or saline implant sized to match the expanded space.
There is no universal timeline for when the exchange happens. Some surgeons schedule it a few weeks after full expansion, while others wait several months. If radiation therapy is part of your cancer treatment, the timing becomes more complex. Radiation affects skin elasticity and healing, and reconstruction failure rates range widely, from 0% to 40%, depending on whether radiation is delivered to the expander or the permanent implant. One study found that waiting longer than six months after completing radiation before the exchange surgery cut the rate of failed reconstruction roughly in half compared to exchanging sooner.
Self-Controlled Expanders
A newer alternative eliminates the need for repeated office visits to get filled. The AeroForm system uses carbon dioxide gas instead of saline. A small gas canister is built into the expander itself, and you control the expansion at home using a handheld remote. Each press of a button releases 10 cc of gas. You can give yourself up to three doses per day, spaced at least three hours apart. This puts you in control of the pace, letting you expand based on your own comfort level rather than a fixed office schedule.
What Can Go Wrong
Infection is the most common complication. Reported rates range from about 2% to 25%, a wide range that reflects differences in surgical technique, patient health, and whether radiation is involved. In one large study, 17% of patients developed an infection after expander placement, and about 13% ultimately needed the expander removed because of it.
Radiation therapy significantly raises infection risk. Patients who received radiation before their permanent implant was placed had an infection rate of about 21%, compared to roughly 10% for those who received radiation after. Other possible complications include fluid buildup around the expander (seroma), skin breakdown over the device, and capsular contracture once the permanent implant is in place.
Using acellular dermal matrix with the expander shifts the complication profile somewhat. It slightly increases rates of seroma and skin flap problems in the short term, but it lowers capsular contracture and the need for later revision surgery. In studies comparing the two approaches, late revision rates dropped from 27 to 53% without the matrix down to about 11% with it.
What the Experience Feels Like
The expansion phase is often described as a feeling of tightness or pressure in the chest that builds after each fill and gradually eases over the following days. The first few fills tend to be the most uncomfortable as the tissue begins to stretch. Most people manage this with over-the-counter pain relief. The expander itself feels firmer and less natural than a permanent implant, which is one reason the exchange surgery exists. Once the permanent implant is in place, the breast typically feels softer and looks more natural than it did during the expansion phase.