I live on the 3 floor of a condo building on the ocean in NY. I have a walkin closet packed with clothes, shoes, etc. that has one wall next to a bathroom and the other is an outside wall. The outside wall had all bricks and insulation removed for about a year (they did the entire building) and now all have been replaced. My wife noticed that three of her rarely used outfits had white powdery stains all over their lining. There is no odor at all.
What do I do? A cursory look shows no stains on the walls nor on other clothing. Should I remove all clothing items for a closer look at them and the walls? Should I do anything inside the closet? Bleach? Heat lamp? Dehumidifier? Some commercial product?

Thanks for input.

most likely this is nothing more than dust, you said the outfits are rarely used.

I also agree it could be dust. I find dust a lot on clothes i rarely wear.

Thanks... The cleaners said that it was definitely mildew... smelled like it. We'll remove all the clothing and shoes over the weekend when we have some time and look for signs on the walls... The outside wall has been rebricked and reinsulated and the humid weather of the summer is over. I'm surely happy to wipe it down, put some product in it or even buy a small dehumidifier. I want to avoid pulling down the walls and replacing them. Any thoughts on that??

Thanks again.