Breast asymmetry

A woman with asymmetrical breasts models a bikini.

Breast asymmetry is found in the vast majority of women (more than 90%, by some estimates) to a more or less visible extent. Size differences can vary for any number of reasons. Depending on the extent of asymmetry, there may be medical issues, including increased breast cancer risk.

Frequency of occurence

Since more or less noticeable breast asymmetry is found in more than 90% of women, it is the rule, rather than the exception. Asymmetry can manifest itself in the size of the breast, the position of the nipple and areola, the angle of the breast, and the position of the breast fold/root (where the breast meets the chest). The left breast is on average larger than the right (due to the left breast's proximity to the heart; protective tissue over the heart along with increased vascularity both project the breast outward and increase its growth).

Asymmetry in breast volume of at least one cup size difference is experienced by up to 25% of women. And for approximately 10% of women, breast asymmetry is greater than that. .

Causes

Breast asymmetry may temporarily or permanently grow more or less pronounced, or even emerge at any point in an individual's life for a multitude of reasons:

• Shifting hormones (puberty, pregnancy, menstrual cycle, menopause, hormonal birth control)
• Water-retention (due to high-sodium foods)
• Weight gain/loss
• Ribcage asymmetry
• Genetics/random growth patterns
• Medical conditions (such as virginal hypertrophy)
• Previous surgical procedures

Medical implications

Regardless of whether or not breast asymmetry is altered, it may still affect development of breast cancer. Studies have found that level of asymmetry within the breasts is a significant predictor of breast cancer development, such that the greater the asymmetry, the greater the likelihood of developing breast cancer. For each 3.38 ounce increase in breast asymmetry (as measured by mammogram), a 50% increase in breast cancer risk was predicted.