What Might Cause a Dull Ache under My Armpit Without a Lump?

There are several things that might cause this kind of discomfort. One possibility is nerve irritation or compression. For example, some studies have shown that pain in the armpit can be an early sign of issues with the nerves in the upper back and chest. This means that the pain might come from a problem near the nerve roots rather than from a lump in the armpit. Another possibility is axillary web syndrome, which happens when tighter bands of tissue form under the skin after certain injuries or sometimes even exercise. This can cause a discomfort that feels like a pulling or aching under the armpit, even if you cannot see any lump. On rare occasions, sometimes cancers can initially show up as pain before a lump is felt. However, in most cases, a dull ache like this is more likely related to muscle or nerve issues. If the pain continues or gets worse, it is important to talk to a healthcare provider to find the exact cause.