A bump in your armpit may cause discomfort, especially if the bump is large enough to cause friction. A bump can develop in your underarm for a number of reasons. In order to determine the exact cause, your doctor may order or perform special testing to identify the problem.
Depending on why the bump has formed, it may be an internal bump that cannot be seen, but can be felt. The bump could be an external bump that you can see and feel. It may be red or pink and tender to the touch. The bump may also feel hot when you touch it, this is usually an indication of infection. While the bump will have some degree of hardness, it may either be very solid or have a slight squishing to it.
A number of conditions could cause a bump to form in your underarm such as a pimple, boil or a cyst. Cysts can be benign or malignant. The only way to know for sure if it is cancerous is to have additional testing performed on the cyst once it has been surgically removed. Pimples and boils can form due to an ingrown hair, infection or from dirt, sweat and debris clogging hair follicles. Certain viral infections, such as AIDS or chickenpox, can cause a bump to form in your underarm, according to the University of Maryland Medical Center.
The size of the bump will vary depending upon the cause. A pimple is typically much smaller than a boil. A cyst can vary in size depending up on the rate at which it's growing and what stage it's in, whether beginning, middle or end. If the bump forms due to a viral infection, it may just barely protrude from the skin.
If the bump looks like a pimple, do not attempt to pop it. If it's a pimple, you can spread the pus to other areas of your skin, which could cause more pimples to form. If the bump is caused by a viral infection, such as chickenpox, it could result in scar tissue, which would leave you with thick skin in your underarms or possibly a scar. Never attempt to pop a boil. Boils should be professionally drained in a sterile environment.
If you're unsure as to why a bump has suddenly appeared under your arm, do not try to treat it at home. Contact your health care provider for a professional diagnosis. If your health care provider prescribes a medication, follow all physician instructions. If the bump has to be surgically removed, ask your health care provider about any concerns that you may have regarding the procedure.