Wash towels immediately if possible (don’t leave them damp in a hamper).
Use the hottest water safe for the fabric (check the care label).
Add 1/2 cup white distilled vinegar to the wash.
Run an extra rinse cycle.
For persistent mildew odor, add 1/2–1 cup baking soda to the wash.
For heavier odor, use oxygen bleach (sodium percarbonate) per label directions.
If the towels tolerate chlorine bleach, use 1/2 cup bleach in the wash per label directions (only for white towels).
Avoid mixing vinegar with chlorine bleach in the same wash.
Dry towels completely in a dryer on high heat; ensure they are fully dry before storing.
If using a line, dry in direct sunlight and keep them separated from damp items.
Clean the washer regularly (run a hot empty cycle with cleaner/bleach/vinegar per manufacturer guidance).
Remove any mildew buildup from the washer gasket and dispenser.
Use a clean, dry storage area; don’t store towels while damp.
Consider using a laundry deodorizer/odor eliminator labeled for mildew on towels, following the label.
Rewash if any odor remains, repeating vinegar/baking soda/oxygen bleach as needed.