Shower curtains can become subject to large accumulations of water and soap, the perfect ingredients for mold and other fungi to feed upon. Over time, you may notice pink patches of mold growing on your curtain. It may be a pink mold variety such as Fusarium or it may actually be bacteria (commonly mistaken for household mold) called Serratia marcescens. Whatever the problem, you can fully clean up the problem using natural disinfecting solutions.
Remove the shower curtain from its rod and gently place it in a washing machine. Place a couple of towels in the wash beside the shower curtain. The added protection of the towels prevents the shower curtain from crinkling.
Add 1/2 cup of liquid laundry detergent to the detergent dispenser and pour 1/2 cup of baking soda directly into the wash. Sodium bicarbonate (the main ingredient in baking soda) not only freshens laundry but also kills mold and mildew.
Turn on the machine using warm water and a "Gentle" setting. Many shower curtains are machine-safe but they are still delicate and require special care. See "Tips" if your shower curtain is not machine-safe.
Pour 1 cup of distilled (white) vinegar into the machine at the start of the first rinse cycle. The acetic acid from the vinegar will react with the baking soda and kill off the pink mold even more effectively.
Remove the curtain at the end of the wash cycle and allow it to hang dry. Do not, under any circumstances, place the shower curtain in the dryer. If any pink mold remains, try washing the curtain again but add 1/2 cup of bleach and 1/4 cup detergent to the wash, instead of vinegar and baking soda. Bleach is another powerful mold killer.