According to the internet, when confronted with a shower curtain that has become icky with accumulated dirt, limescale and hard water deposits, mildew and mold, soap scum, and serratia marcescens bacteria (!) … many people will just throw it away and buy a new one. Even members of my own family would do this!
However, a spin in the washing machine will make a shower curtain as good as new and repeated washings can add months or even years to their useful lives. Just put them into the washing machine with a few heavy towels (especially for top-loading machines, which can tear up shower curtains without the towels to act as padding and buffers) and add the usual amount of detergent. As a booster, add about a half cup of ammonia (my favorite), or some baking soda, borax, vinegar, or bleach. [Of course, never use ammonia and bleach together.] Run the machine on the longest cycle with hot water. You might pause the machine for some additional soak time. There’s no need for a high-speed spin. Don’t put the shower curtain in the dryer. Just re-hang it in the bathroom and admire it as it dries.
You can also admire the money that stays in your bank account each time you do this. A new shower curtain might cost at least $8. Washing it in your home washing machine costs about 50¢.
If you have a mildew, mold, and serratia marcescens problem in your bath and shower area, a fan in the bathroom might help.