system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: does bleach remove stains in their entirety or just masks the color?

I had a severe nosebleed two nights ago that got on my white pillow sheets. I threw them in the laundry this morning but forgot to use bleach, which resulted in them having some dark stains.

I threw them in the laundry again but with bleach and the stain went away. So what does bleach actually do? Does it remove the stain (dried up blood, etc) or just removes the color (dried blood is still there)?
gpt
Many of the stains we get on clothing are due to organic molecules, little groups of atoms bound together in particular structures.  Because they are rather large and sticky, they get stuck in the fibers of clothing or carpet and make stains.

Bleach is a strongly reactive substance, meaning that it interacts with the stain molecules.  Frequently it breaks the bonds holding the atoms in the stain molecules together, tearing them into smaller pieces that aren't colorful anymore.  These are washed away in the laundry.

There may be traces of the blood left, but most of it was chemically digested (broken apart) and washed away.