Lief is suitable for those ages 13 and up. Lief is an FDA class II medical device that has passed FDA testing requirements for cytotoxicity, sensitization, and irritation. Lief’s ECG technology is widely used and very safe. There is no risk of electrical shock because your Lief does not emit any electricity. Rather, it records the electrical activity of your heart. Although the Lief stickers are designed for sensitive skin, in rare instances they may cause minor skin irritation, such as redness or itchiness, which subsides after discontinuing wear. There are no other known risks associated with using Lief.