I'm having a little trouble finding a deodorant that I like. The problem is that they all leave white marks in my t-shirts. I've tried different brands and I always pick the one that claims to leave no white marks, so I really don't get it. So what I wanted to ask is what causes the white marks? Does it make a difference wether you use a spray, a roll-on or a stick formula? Are they're certain ingredients you have to avoid to prevent them? And is they're a difference between regular deodorants and anti-transpirants when it comes to white marks?
I hate those white marks too. Usually the Secret gel antiperspirant doesn't leave white marks. I have to let it dry before I dress. I also use Secret Clinical Strength. I follow the directions and put it on the night before. When I dress in the morning it still gives protection but does not leave white residue.
Actually, Consumer Reports (not your usual source for beauty tips, I know!) cites a recommendation from the American Academy of Dermatology to apply even regular antiperspirants at night. This makes the product work more effectively, as more product is drawn into the pores to reduce or stop sweating. "The effect lasts 24 hours or longer, even after morning bathing," according to the article (July, 2009 issue, page 12). So I second bluecatbaby's suggestion to apply antiperspirant, regular or clinical strength, before bed to reduce the white marks. The added benefit is a more effective usage of your antiperspirant.
Sorry, I can't address the other questions in kitten's OP.