Make sure deoderant is dry before wearing clothes. If excess perspiration is the cause, see your doctor about possible treatments.

I HATE this. I sweat quite a lot, mainly due to hormones my doctor says, and i wear a lot of white. My tops start to stain even after i have only worn them a few times. You can buy protective pieces of material that go into your clothes and absorb the sweat and staining chemicals, though this doesnt quite work for your cute little vest tops or my nice new off the shoulder tshirt. I tried products such as perspirex too that aim to keep you from sweating by "sealing"sweat glands, rather than just blocking them with something powdery. The manufacturer recommends using it daily for a while, then only weekly. It did work for me, although i had very itchy and irritated armpits!