After a while I began to get small painful lumps under my armpits about once every two weeks or so. They last about a day and then disappear. I started using deodorant again but I keep getting them.

armpits, and groin. A swollen lymph node may be painful and tender to the touch. In some cases, it will be visibly enlarged under the skin, but in others, it will be smaller or deeper in the body ...

Or, your healthcare provider may need to drain the bumps if they're large and painful. You can get heat rash in your armpits when sweat glands get blocked and sweat builds up under the skin.

Painful armpit lumps are often due to a swollen axillary lymph node under the armpit. This is usually a sign that the body is fighting an infection, but it can sometimes indicate cancer.