It is not unusual for one breast to be bigger than the other. Almost every woman with natural breasts has a slight difference between the two. One may be larger, higher, have a different shape etc. That is what makes you human and not a robot.
There are many explanations for this, here are a few;
1. For young girls, rapid growth that occurs prior to and during puberty is one reason one breast might be bigger than the other. Often, the smaller breast catches up in size with the larger one later in development.
2. For grown women still having their menstrual cycles, the breast could react to large amounts of estrogen that are released in cycles, and also to disruptions in the cycles. This can cause the breasts vary in sizes.
3. If you have been on the big side for a while and you decide to lose some weight it’s normal to lose some fat around the breast too, and the same applies for those who gain weight.
4. Pregnancy and breastfeeding can also bring changes in your breast size. If your baby sucks on one breast more than the other, the most active breast would produce more breast milk which would make the breast heavier and bigger.
5. For some women the left breast is bigger than the right. This is due to the breast proximity to the heart and a greater number of arteries and veins, along with a protective layer of fat surrounding the heart located beneath it.
This is for general informational purposes only and is not a substitute for professional medical advice. If your asymmetrical breasts are more than slight, then it maybe necessary to see your doctor.