If your cotton T-shirts have a mildewy smell that isn't being eliminated by detergent alone, there are a few additional steps you can take to help remove the odor:
Vinegar: Add half a cup to a cup of white vinegar to the washing machine during the rinse cycle. Vinegar is known for its odor-eliminating properties and can help remove mildew smells from clothing. Avoid using vinegar with bleach or ammonia-based products.
Baking soda: Sprinkle baking soda directly onto the mildewy-smelling areas of the T-shirts or add half a cup to a cup of baking soda to the wash cycle along with your regular detergent. Baking soda helps neutralize odors and can be effective in removing mildew smells.
Oxygen bleach: Consider using an oxygen bleach product, such as hydrogen peroxide or oxygen-based bleach powder, following the manufacturer's instructions. These types of bleach are typically safer for colored fabrics and can help remove stubborn odors.
Sunlight and fresh air: After washing, hang the T-shirts outside in direct sunlight. Sunlight has natural disinfectant and deodorizing properties that can help eliminate mildew smells. Make sure to avoid prolonged exposure to direct sunlight, as it may cause color fading.
Remember to always follow the care instructions on the T-shirt's label and test any new cleaning method on a small, inconspicuous area of the fabric before applying it to the entire garment.
If the mildew smell persists despite your attempts, it's recommended to consult with a professional cleaner or consider replacing the T-shirts if the odor cannot be removed.