What might cause sharp pain under my left armpit and the side of my breast?

There are a few potential reasons for experiencing sharp pain in these areas. One possibility is nodular fasciitis, a benign condition where a small lump of tissue develops in the axillary tail of the breast. Although it is not cancerous, this growth can cause a sharp, localized pain. Another explanation might be axillary web syndrome. This condition involves the formation of tight, cord-like bands under the skin which can sometimes occur even without surgery or other interventions. These bands may shorten or tighten, pulling on the tissue and causing a sharp, sometimes sudden pain that radiates from the armpit to the side of the breast. In some cases, similar pain may also be seen after procedures involving the armpit, where needle placement or manipulation of the lymph nodes contributes to discomfort. If the pain is persistent or if you notice any new lumps, swelling, or other changes, it's important to see a doctor. To better understand what might be causing your symptoms and get personalized insights right away, you can check your symptoms with Ubie's free AI-powered tool. They can help you evaluate your symptoms and determine the next best steps for your care.