What can cause a bad smell in a woman's vagina?

Bacterial vaginosis: Most commonly: a ph imbalance resulting in proliferation of a certain (normal) bacteria all women have in the vagina. It could also be: trichomoniasis (which is sexually transmitted), but BV is most common. Easily treated with antibiotics. Or could try boric acid vaginal suppository from a compounding pharmacy (but i think you still need prescritpion).