Is This Underarm Lump Serious? Five Ways to Tell

by PJ Hamel Patient Expert

You notice a lump in your armpit - something that wasn't there before. Don't panic - but don't brush it off, either. This simple checklist will help you determine whether or not to see the doctor now, or wait until later.

Did you know that your breast tissue extends up into your underarm area? And that your underarm harbors a cluster of lymph nodes, nodes that can become cancerous? And that, therefore, an underarm lump can be a symptom of breast cancer?

No, I didn't know that, either. But as a well-read breast cancer survivor, I've learned a lot over the past 12 years. And a lot of what I've learned is when to pursue diagnosis and treatment - and when to simply wait.

An underarm lump, like a mysterious lump anywhere on your body, can be scary. But rather than worry yourself sick, ask yourself the following five questions; the answers will help you determine just how serious that lump might be, and whether to call the doctor.

Is the lump new? Or has it been there for years, without changing?

If the lump you feel has remained the same size and consistency, in the same spot, for years, then it's probably just scar tissue, or a natural part of your anatomy. Lumps that are cancerous will grow in size as time goes by; or produce other, secondary lumps.

Have you been ill lately?

The aforementioned lymph nodes are your body's cleansing system; they filter out and fight any abnormalities in your lymphatic system, including cancer cells, infections, or even cells damaged by adverse drug reactions.

So, if you've had the flu or some other systemic infection (e.g., shingles, mononucleosis, chickenpox); or if you injured the area (an insect bite, a nick while shaving, even severe sunburn), you might very well have a swollen lymph node or two as a result of the "battle" going on between your lymph cells and the alien invaders. If indeed you've been sick or injured, wait a couple of weeks to see if that lump starts to shrink; if it was illness-related, it'll eventually disappear.

Have you had a recent vaccination? Are you allergic to any medications?

Vaccines for smallpox, typhoid, and MMR (measles/mumps/rubella), as well as reactions to penicillin and iodine, can cause underarm lumps. If you've recently been vaccinated, or may have had an allergic drug reaction, let your doctor know - but it's probably safe to simply wait it out.

Is the lump red and painful? Is it growing noticeably, day by day?

Cancer doesn't grow nearly as quickly as an infection, nor does it cause skin redness. If the lump you have feels and acts like a pimple -
then that's probably what it is, a localized infection. Keep the area clean and dry, and apply warm compresses; if it doesn't start to abate in a couple of days, see your doctor for treatment.

What does the lump feel like?

An infected lymph node will usually be fairly soft, painful, and moveable; you can push it around a bit with your fingers. A cancerous lump is more likely to be hard, painless, and fixed in place. It may also feel like it's connected to other, smaller lumps.

So, bottom line: If the underarm lump you feel is red and/or painful, and growing noticeably, see your doctor. Or if you have a new lump of any kind that doesn't disappear within a few weeks, see your doctor.

But if the lump you feel doesn't grow larger, and then disappears on its own within a few weeks, it's probably safe not to pursue diagnosis and treatment.

PJ Hamel
Meet Our Writer
PJ Hamel

PJ Hamel is senior digital content editor and food writer at King Arthur Flour, and a James Beard award-winning author. A 16-year breast cancer survivor, her passion is helping women through this devastating disease. She manages a large and active online survivor support network based at her local hospital and shares her wisdom and experience with the greater community via