How to differentiate between an ingrown hair, razor bump, cancer, or lymph node?

Ask your doctor: A superficial lump in an area in which you shave is most likely an inflammatory reaction to the irritation from shaving, or from a blocked hair follicle. Cancer is unlikely, and lymph nodes are not superficial. Also ingrown hairs and razor bumps likely come on quickly and will go away if you leave them alone, but a cancer won't. See a dermatologist for proper diagnosis.