My 93 year old mother in law is developing blisters on her thighs and behind her knees. she is not bed ridden and the location does not seem to be consistent with pressure. They don't hurt and there is no rash, but they are large and when they rupture, we must be concerned about infections. Her MD thought they were pressure blisters, but that does not seem to be the case. She has congestive heart failure and some renal problems related to age.