You should be able to get 15 or more uses from each pair before having to get more. But you have to do your part. Here’s how:
1. Keep them away from heat and cold. That means out of the sun, away from the cold. Just keep them at room temperature.
2. Store them on the plastic backing sheet, and keep the plastic bag sealed. You don't want them to dry out, so keeping the bag sealed will preserve moisture (I'll tell you how to re-hydrate them, or put the "bring the stickyness back" in a second…).
3. Here's the big one: keep lotions, oils, grease, sweat, dirt, lint, etc. off of the sticky side. Contaminating the sticky gel part will make it, well, not sticky. So, just make sure the skin is free of sweat, lotions, skin oils, etc. and try not to drop the electrode pads in a huge pile of dryer lint!
4. If the sticky side starts loosing the stickyness, you can revive it a few times before having to replace the pads. It's easy, just take your finger, pass it under some running water, and wipe a little bit on the sticky side of the pad. The water will soak in and re-hydrate the surface, giving the pad some extra life!
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