1. About 20 times. They can be reused. You can use it until TENS pads are not sticky. After each use you can stick them onto the plastic sheet that they originally came with.
2. They will last as long as you can keep them sticky. Over time they will either pickup too much residue and/or dry out. Keeping them stored in the bags when not in use will prolong life. You can gently rinse the sticky side with water and let dry for a day, while stuck to the plastic storage square, to remove excess dead skin, etc. This will prolong their life once they start to loose their stick. It has also been reported that you can use an essential oil to keep the sticky side hydrated and clean prolonging life.
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