Sponges are full of holes and crevices that food gets nice a stuck in. It’s recommended that you soak your sponges in bleach once per week.
Better kill ALL the germs so you won't get harmed any time!!!!!!!111
(Might affect your immune system and cause allergies, but what the heck, hygene product manufacturers have to earn their money, don't they?)
Regards
Your hygene industry