The thongs I use for sport with leggings and work are a mix of polyester and spandex. I want them to last as long as possible.
I experimented a bit with one: I made a baking soda paste, applied it to the stained parts, let it sit for an hour, hand scrubbed it, rinsed in cold water, pressed the thong to get rid of as much water as possible, let it to air dry. Am I being too careful?
Baking soda removed all stains.
Do you only hand wash your undies?
I think that the answer to that is a solid “maybe”. Damage to materials by energy (heat) is a two dimensional thing; energy input and time. Before a certain temperature threshold, your thought probably is correct. Whether that threshold is equal to the settings available on your dryer and whether it is practical are further questions that will probably vary with the fabric in question.