
Originally Posted by
thisAngelBites
It could be a lipoma (basically a little localised blob of fat that is not dangerous - some people are more prone to them than others, they are permanent and need to be removed if they bother you), it can also be the result of a viral infection (and so it would go away in time) or it may be a cyst (these tend to not be fixed to underlying tissue, and so you can sort of wiggle them around). As LT75 said, sometimes antiperspirants can cause blocked hair follicles or sweat glands. It could also be a swollen lymph node from you fighting off a recent infection.
Very rarely, these lumps can be signs of something more worrying. Just to reassure yourself, you should get a doc to have a look and feel, if it doesn't appear to be going away soon.