Please get to a doctor right away--not because it's dangerous, but because a blistery eruption could conceivably be herpes and the best way to get a clear-cut diagnosis is to have a doctor see it and perhaps culture it.
On the other hand, it could be something else entirely--perhaps an irritation of some kind, or even waterlogged skin.
Either way, diagnosis and treatment will require examination. The sooner the better.
Best.
Dr. Rockoff