Hi I Have Been Having A Red Rash Under One

hi I have been having a red rash under one arm pit sporadically this past month. Each time seems to be a little worse. today it is showing blisters. I can't relate it to allergens. I don't use a razor I have been using hair removal cream for years without any problems. The rash is between a burn and an itch and it leaves a bruise when it clears up. Is this reason to be concerned?