What might be causing a dull ache under my left armpit?

There are several reasons why you might feel a dull ache in your left armpit. One possibility is muscle strain or inflammation from everyday activities, which is common and usually temporary. If you've had surgery in the area, such as axillary lymph node dissection during breast cancer treatment, the pain might be a long-term side effect where the lymph nodes or surrounding tissues remain tender. Another explanation could be referred pain from the chest. Sometimes, heart-related issues, as seen after procedures like coronary artery stent implantation, may send pain signals that are felt in the armpit. There are rare cases when infections or conditions like Lyme disease might affect nerve areas and cause discomfort, though this is less common. If the dull ache goes away with rest and over-the-counter pain relief, it's usually not a cause for concern. However, if the pain sticks around, gets worse, or you experience other symptoms like chest pain, shortness of breath, or fever, you can check your symptoms with our free AI-powered tool to better understand what might be causing your discomfort and whether you should seek immediate medical attention.