There are a variety of processes performed by plastic surgeons to improve the look of the breasts such as augmentation (implants), a lift, and reconstruction.
Breast augmentation is a sort of operation where implants are put inside to make them seem larger. Many girls with a smaller bust seek out this type of procedure to have firmer and much more voluptuous appearing breasts.
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Some women have difficulty fitting into certain forms of clothing because of their bra size and others feel self-conscious or downright embarrassed at the sight of the little bosom whenever they wear tight or revealing clothing such as tank shirts, summer dresses, or swimwear. These are also a legitimate reason for wanting to have this particular operation.
The number one reason for women for wanting this breast surgery would be to change little flat breasts into the larger more womanly looking bosom.
Size isn't the only one thing which you will need to think about. Some girls do not like the shape of the bosom either. If you long for fuller and rounder breasts afterward implants may make this a reality for you.
If they are asymmetrical or lopsided then is another reason. It's been speculated that both breasts on a woman are not the same anatomical size but for most females that difference is hardly noticeable.
However, if yours have a definite difference to them that is evident to you breast surgery can fix this problem. The same can be said of congenital deformities.