Finding lumps anywhere on the body can be a potentially scary development, but if those lumps are underarm cysts, the problem generally is more annoying than dangerous to your health. The term "cyst" actually comes from the Greek word "kystus," which means "bladder" [source: University of Rochester]. In this case, the term bladder just refers to a sac -- particularly a sac beneath the skin containing pus, much like a common pimple [source: MedlinePlus: Sebaceous].
This sac forms when some of your epidermal skin cells don't slough off, but instead move down under the surface of your skin and begin to grow there. This often happens as a result of a hair follicle or an oil-producing sebaceous gland within the follicle becoming damaged [source: Mayo Clinic]. On your face, for example, acne might cause such damage. In your underarms, shaving might be to blame. But any kind of damage to the skin, such as a wound or exposure to harmful ultraviolet rays, can create the conditions that form a cyst [source: Mayo Clinic]. Even being a male raises your chances of getting one, because men are twice as likely as women to develop cysts [source: Hanson].
Once the cyst starts to grow, it forms a small sac that fills up with a protein called keratin that has a yellowish color and foul odor. This sac grows to create a small protrusion on your skin at the source of the initial injury [source: MedlinePlus: Sebaceous].
Although the armpits are a sensitive area of the skin, most cysts are harmless, painless and can actually be left untreated. But if you develop a cyst and it bothers you for cosmetic reasons, or worse, if it becomes infected, you should see your doctor.
Read on to discover ways of diagnosing and treating underarm cysts.