These patches will self-heat up to 58 degrees Celsius once opened, so should NEVER be applied directly to the skin. Instead, stick the two adhesive side flaps to your clothes to allow the benefits of heat to safely warm through. Helpful in alleviating arthritis, lower-back pain, period pain, stomach ache and rheumatism. Also great for fishing, hiking, skiing or any outdoor activity where you need a bit of warmth. The non-woven fabric will not leak and has high air permeability, meaning the heating process is not activated until the outer pack is opened and exposed to oxygen. This process will continue for up to 8 hours, after which it can be safely disposed.