Two Year Old Boy With Rash (blister Like) Covering His

Two year old boy with rash (blister like) covering his butt and genital area, legs, elbow. Reacurring!!! Recently had hand foot and mouth virus. Never completly healed all sores and now is breaking out again. No apparent sores to mouth/face currently but legs, butt amd elbows covered heavily. Is this same virus? Should i be concerned? What can i do for him?