Skin underneath a ring was red, itchy. last week or so it became blistering, painful, peeling. getting worse. what could it be?

Dermatitis: Rashes under rings can be due to metal allergy (contact dermatitis), or an irritant effect from soaps trapped under the ring if not removed when doing dishes without gloves. Both causes can get secondarily infected, with germs, or yeast, giving much redness and tenderness. Remove the ring before dishwashing and get appropriate cream from a dermatologist.