We had some drenched towels that laid on our bathroom floor for a few days. They were balled up, and started smelling musty.
Yesterday morning, I hung the towels up outside on a swingset. It was a bright cloudless morning, and the towels were bathed in sunlight for five straight hours or so. Not particularly breezy. I came home for lunch and went into the backyard to check on the towels. They were bone-dry and smelled pretty good. Not a frou-frou fabric-softener scent, but a mild, fresh “outdoor” scent (faintly like grass, I guess).
OK. I knew the sun would dry the towels out … but what happened to the mildew odor? What was going on at a microbiological level?
IAMNAmicrobiologist (and hoping a real one comes along later), but
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Sunlight has a lot of UV, which not only sunburns your skin, but is also a strong anti-bacteria method. Biology labs use UV lamps at night to make sure that their used petri dishes et al are bacteria free.
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If there is grass underneath, the sun shining on it will create oxygen, which acts like bleach (that’s why people put linen on dewy grass outside).
The fresh smell itself, I can’t explain where it comes from, but I really like it. Of course, I dry outdoors whenever the weather allows it (indoors when it rains - clothes dryers are a waste of electricity, in my opinion, only suitable for emergencies).
Thanks, constanze. What I really found startling was how fast the towels freshened up, and how thoroughly. They were pretty rank when I hung them up 
UV from sunlight plus simply drying the towel does a pretty good job at killing mildew. Remember, mildew likes damp, dark places. Sunlight is generally a fairly effective microbicide, though there are plenty of microbes that survive just fine under direct sunlight. But the sorts of microbes that we don’t like, including mildew and many pathogens, don’t have the same adaptations that allow survival in outdoor microbes.
A month ago one of my cats got upset and urinated on top of my Queen sized bed with one of those 3" thick memory foam mattress covers and comforters. The bed itself wasn’t damaged because the memory foam soaked it up like a sponge and my GF was quick to get it off the bed and into the yard. She ordered me to pitch it, declaring that no amount of cleaning could bring it back in her mind. :eek:
Still I pursisted to try and salvage the thing as I would definitly want to have one just in case it happened again (a new one runs $175); so washed it down with the hose and poured a gallon of diluted lysol on the thing. After 5 days of laying in the 95 degree sun and constant washing, turning and ringing out my GF declared it safe to lay upon again. The sun is a mighty thing, even cat piss can’t stand up to it. 