Why is it that washing bloodstained fabric with cold water helps to remove the blood, but washing with warm or hot water causes the stain to set?



It seems like most fabric stains come out more easily with hot water. Is blood just weird?

In: Biology

Think of taking a cold shower vs a hot shower. A cold shower makes you want to get out as soon as possible, while a hot shower makes you want to relax and stay in as long as possible.

This is how the proteins in our blood react to water. When the blood first contacts our clothes it dries up and attempts to hold on to the fabric of our clothing. The cold water penetrates and rehydrates the blood encouraging it to wash away. Hot water accelerates the binding process and allows the blood to cling onto the fabric faster, making it harder to wash away later.

Cleaning protein stains can be thought of like cleaning a raw egg white off of a rag.

If you use hot water the raw egg white will cook enough to set into the cloth. You can’t just rinse out the egg white if it’s been turned into cooked egg white all imbedded around the cloth fibers. It’s *much* harder to get out after the proteins are heated. Same with blood.

That’s also why you always want to check on a stain *after* it comes out of the wash. Because once you put it in the dryer it’s probably never coming out.

But for some things, like blood and grass stains, if you soak it with an enzymatic stain remover (like Shout™) for long enough the enzymes will eat the protein and it’ll still wash out.

*If you want to see what’s happening on a more molecular level, take a handful of thin rubber bands. Gently mix them all together into a cohesive pile. Each rubber band represents a protein strand.

You could untangle this pile.

But not after you blast it with a hot hair dryer. That pile is not untangling ever again.