Food grade silicone is nonporous which inhibits bacterial growth and odors. However, some foods or dishwasher detergents can retain an odor.For dishwasher detergents, It is best to choose dishwasher soap or detergents that do not contain essential oils, antibacterial agents or moisturizers. Gentler, more natural dishwasher soap/detergents work best to clean Zip Top containers, especially ones that are scent free. For food odors, try rubbing with a baking soda and water mixture and let sit for 4 hours. Rinse well and then wash as usual.