Sudden sharp pain under the left breast in women is often related to noncyclic breast pain, chest wall pain, or pain that comes from the lungs or heart. It may feel stabbing, burning, or tight, and it can be brief or come and go.
A common cause is irritation or inflammation of the muscles, ribs, or cartilage in the chest wall, especially if the pain worsens with movement, pressing on the area, deep breathing, coughing, or sneezing. Breast pain itself is usually benign, but focal pain on one side can sometimes need evaluation, especially if it is new or persistent.
Pain that starts suddenly and worsens with breathing can also come from the lining around the lungs. Because left-sided chest pain can sometimes be related to the heart, it should not be ignored, especially if it comes with shortness of breath, sweating, dizziness, nausea, pressure in the chest, or pain spreading to the arm, back, neck, or jaw.
Avoid self-medicating, especially if the pain is severe, new, or associated with other symptoms. Seek urgent care for severe or concerning chest pain, or see a primary care doctor, gynecologist, or cardiologist for evaluation.