It just doesn't. This is simply a lie, and I actually took a day off to trace it back to the person who started it -- it turns out they were trying to sell their own brand of deodorant by claiming the others cause cancer. Frankly, you need to be able to recognize quacks. Do you think the folks at the NIH would use deodorant if it were unsafe? They're the ones who'd know. For your own survival, be discerning.
No , not really. There is no conclusive research linking the use of underarm antiperspirants or deodorants and the subsequent development of breast cancer.Or cancer. Read this at: http://www.Cancer.Gov/cancertopics/factsheet/risk/ap-deo.
Pretty unlikely. This myth has been around for a while. No substance to it.