Ruin your posture
Wearing the wrong size can ruin your posture and give you pain in the shoulders, neck and back, forcing you to bend and prevent you from having good posture.
Pinched skin and scars
If your bra is too tight, this can cause the underwire to poke you or leave marks around your ribcage, which can lead to scarring if it continues.
Breast cancer
When you wear the wrong size bra, one that is too tight, this can block blood flow of the breasts, which can cause cancer. It can also cause blockage of the lymph nodes, which are sensitive to pressure and putting pressure on the breasts can cause lymph nodes and vessels to close.
If you feel uncomfortable with a stranger fitting you for the right size bra, you can do it yourself. See below: