Lifting weights comes with myriad benefits. Chief among them is strength, but resistance training also can improve balance, enhance mood, increase caloric need and even prevent bone loss. That being said, lifting weights has its own set of safety concerns. Developing a cyst in the armpit isn't usually one of them -- at least not directly. Talk to your doctor to determine the exact cause of the lump.
The lump in your underarm may be nothing more than a clogged sebaceous gland. If, for example, you wear antiperspirant while strength training, the aluminum-based compounds responsible for keeping wetness at bay can also clog your pores. When a clog forms, the associated gland can become irritated and inflamed, resulting in a cyst-like lump in your armpit.
Sometimes, heat rash can develop into a cyst-like lesion in your underarm. Friction from clothing, especially when tight, can lead to blockages within your sweat ducts. This traps perspiration under your skin, resulting in lesions. If a blockage manifests along the very surface of your skin, small blisters form. But when the blockage forms deeper in one of your pores, you can develop a firm, fleshy bump.
The cyst might have nothing to do with weightlifting at all. Instead, it could be a sign of a bacterial, viral or fungal infection. In this situation, exposure to a pathogen causes one of your lymph nodes -- which filter lymphatic fluid and destroy infectious microbes -- to swell, leading to a cyst-like lesion along your underarm.
Instead of a clogged pore, heat rash or infection, the cyst could be a sign of a serious medical condition. In fact, a swollen lymph node is often the first sign of Hodgkin's lymphoma or non-Hodgkin's lymphoma. Don't panic, however. With either of these cancers, you'll likely experience other symptoms, such as fatigue, night sweats, loss of appetite, fever, chills and unexplained weight loss.
If you develop a lump in your underarm, talk to a doctor. It's always best to err on the side of caution when dealing with any lump that develops on your body. Once the cause is determined, your doctor can establish the appropriate treatment plan.