What causes side boobs? I have wide but flat breasts now. I am concerned I’ll get side boobs!

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. This will ensure that you avoid the dreaded "fake" look. 
With regards to your specific question, avoiding "side boob" is contingent upon not exceeding your BWD with a device that is wider than can be accommodated by your chest wall. The best advice is to respect your BWD and "love the look not the cup." 
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

Hi irismustang,

Breast implant type and sizing selection is a complicated process and requires a detailed consultation that includes a discussion of your goals, a detailed examination, and a lengthy discussion. But the decision will always start and end with the patient.

Implant profile is one of the important considerations to make. Many patients wrongly assume that the higher the profile the better. The truth is, the more profile (or projection/height) and implant has, the narrower its base has to become. This is associated with several problematic consequences.

The first issue is that the patient loses width and therefore cleavage of the breast. The second is the breast becomes more narrow and pendulous, often falling lateral and onto the side of the chest, and third, high profile implants have a higher risk of bottoming out because they exert more pressure on the inframammary fold than moderate profile implants.

High profile implants do have a role in symmastia repair (when I need to narrow the base width) but otherwise I try to avoid them.

When it comes to sizing, we have all of our patients find 3 photos of their desired breast size. We ask for naked breast photos because clothing can obscure the true size (push up bras). Next, we consult with patients and go over the photos and take detailed breast measurements during a physical exam. Next, we using a sizing algorithm to determine a range of implants that will work based on the exam and the measurements.

Lastly, during the operation, we use silicone sizers in the operating room to see how the size actually looks in the breast. We sit the patient up in the operating room, while asleep of course, and compare the sizer result with their desired look photos. If it is too small, we start the process over with a slightly larger implant. We don't stop until we get the perfect match.

Of all of my breast augmentation patients, every one of them has been happy with their size due to this detailed and meticulous process. You don't want to invest time and money into a result that is either too big or too small.

You should discuss your concerns with a board-certified plastic surgeon and make sure that your surgeon understands your goals.

Daniel Barrett, MD, MHA, MS

Certified, American Board of Plastic Surgery

Member, American Society of Plastic Surgery

Member, American Society of Aesthetic Plastic Surgery

Hi Iris, 
Breast Implants come in different shapes and sizes. We refer to different shapes as profiles if we are only considering round implants. 
The profile of the implant will decide the width of the breast as well as the projection or how much they stick out. 
Another important aspect is how your chest wall is shapes. it could be flat or concave or convex. 
So choose a couple of plastic surgeons to consult with and then make your educated choice. 
Wishing you a safe and happy surgical experience, 
Tarek V. Copty, MD FACS