Now, the stuff in your medicine cabinet is about 1-3% H 2 O 2 , and that can cause some irritation problems. There's also "food-grade" versions that are much more concentrated, at 35%. You're supposed to only use a couple of drops with a ton of water according to those that advertise its "benefits," but unfortunately that doesn't always happen. Symptoms of ingesting too much range from mild stomach pain and nausea to severe tissue damage and even death.