I would agree with you initially; however, by the time the blisters form the urushiol should be off as it takes 2-3 days for a reaction to occur. I would recommend taking a cold shower if you think/know you came in contact with poison ivy and scrub down with some type of medicated soap. If you still get the blisters a few days later, I don't think it would hurt opening the ol' pores up popping them and treating with ivy dry, jewelweed, etc...