So what causes reactivity? Viruses, for one thing, as well as your menstrual cycle, since there is often breast tissue in the armpit area and that tissue responds to hormones as they cycle. In addition, cuts on your fingers, nicks in your cuticles from a manicure, or a simple scrape on your hand can cause your lymph nodes to enlarge as your body fights off infection. Finally, and most commonly, shaving your armpits can cause your lymph nodes to change because hair follicles can become clogged and slightly inflamed.
