Uneven breast size is very common – most women have uneven breasts. And, your smaller breast is usually on the same side as the hand you write with.
Breast size difference that is greater than one cup size is a little more unusual. In this case, the cause could be attributed to a body injury or illness during breast development. It can also be the result of using one arm repeatedly at work. Uneven breasts can also occur during menopause when hormones can cause your breasts to expand unevenly. If you're an athlete and use one arm more than the other, this too can cause uneven breasts.
Tip: Buy a bra in a cup size that fits your larger breast. You can then supplement the smaller breast side with pads.
Breast Enhancers Most bra styles can be retrofitted with removable pads called “cookies” or “breast enhancers” which add volume to the smaller breast thus giving you an even appearance. Figure out where your fullness is missing in your breast, then put the cookie in the correct place in your bra cup – along the bottom, along the side, or on the top of your breast.
Contour Cup Bras Contour cup bras (seamless cups with a thin foam layer for shaping and modesty) are particularly good for giving you an even look without the need for additional padding – as long as your breast size difference is less than a full cup size.
DD+ Cup Size: Elasticized Top Cup Edge For DD cup sizes (UCS D2) and larger, bras with an elasticized top cup edge (where the upper edge of the cup is elasticized or where the upper fabric is stretchy) will form to each breast for a more perfect and custom fit.