The drain cleaners you can buy at the hardware/grocery store, are basically harmless, and useless. I have NEVER gotten burned or even "scorched" by them. The only way I know they have been put in the drain is because the water feels extra slippery.
Some people are extremely sensitive to it, others not so much.
I use it as cheap degreaser.
It only works on grease or hair, not obstructions.