HI, I've been using the patches for right many years (a heart patient told me about them) after too many years of suffering severe itching on both arms which no dermatologist could help until I found one that did superficial radiation; then he passed away. Anyway, I have never heard that one could become immune. They keep working for me, using them on the same areas over and over. I do know that no more than three patches should be used in a 24 hr. period, no more than on for 12 hrs.; then 12 hrs. off. I have used four at the time twice. My doctor told me of a person who used many all over, all the time, and died! So, everyone, follow the instructions, please!