Pain under your left breast can be caused by a condition called costochondritis. When the cartilage that is located between your ribs becomes inflamed, this results in costochondritis. The ribs generally become inflamed at the juncture where they attach to your sternum or breastbone. Your joints in this area can swell as a result of costochondritis.
According to the Loyola University Health System and Costochondritis.org, this condition can cause pain in your breasts.
Before Your Period
Right before your menstrual period, when there are higher prostaglandin levels in a woman’s body, these prostaglandins can escape into the bloodstream from the uterus and have an affect on your muscles, causing pain in your breasts.
You may feel pain in the front of your rib cage and a dull, aching pain in your chest as well as in your breasts. If you touch your ribs they are sensitive and sore.
Pain in the lower left breast can also be the result of irritation to your chest wall, irritation to the chest wall muscles, or due to pleurisy, which is inflammation of the lining called the pleura, located between the lungs and the chest wall.
Breast pain can indicate something other than costochondritis. Make an appointment with your physician and get an official diagnosis.