Wash your towels in hot water with a cup of vinegar, and then run again in hot water with a half-cup of baking soda. That will strip your towels from all of that residue and mildew smell and will actually leave them feeling fluffy and smelling fresh. (Do not add laundry detergent to either wash. Just once with vinegar and once with baking soda.) good to know for the future.
My mattress had several stains, I'm sure they were a combination of drool, urine, beverages, baby spit up- you name it. Anyhow, this method really worked well. I had one pretty dark stain that I sprayed again later with a new mixture. I am amazed..