What's up with the different grades of H2O2?

Not pure H[sub]2[/sub]O[sub]2[/sub]; water is also present, of course. (To a chemist, the term “pure H[sub]2[/sub]O[sub]2[/sub]” means only that particular chemical species is present, that is 100% H[sub]2[/sub]O[sub]2[/sub].)

“Food grade” hydrogen peroxide is typically sold as 35% H[sub]2[/sub]O[sub]2[/sub], with the remainder consisting of water. A solution of 35% H[sub]2[/sub]O[sub]2[/sub] is still quite concentrated; note that the typical percentage of hydrogen peroxide for antiseptic use is more like 3%.

As others have noted, pure H[sub]2[/sub]O[sub]2[/sub] is exceedingly dangerous. This was discussed in a thread a few years ago, in which I stated: