Scientists took a look at the bras we wear today and have found that the constricting effect of bras could be causing cancer. Specifically, when you wear a tight fitting bra, it suppresses the lymphatic system below the armpits and blocks an internal network of vessels supposed to flush toxic wastes from the body. Over time, these toxins accumulate in the breast tissues and create an environment in which cells can turn cancerous. Moreover, aluminum compounds, parabens, propylene glycol, triclosan and steareths are examples of potentially dangerous toxins found in many common deodorants  that can accumulate if your lymph drainage is impaired.
Scientific evidence does not support a link between wearing an underwire bra (or any type of bra) and breast cancer risk [460 ]. There is no biological reason the two would be linked. Any observed relationship is likely due to other factors.
A 1991 461 ]. However, the authors stated this link was likely due to factors related to wearing a bra rather than the bra itself. The women in the study who did not wear a bra were more likely to be thin, which the authors concluded might account for their decreased risk of breast cancer [461 ].
In an article by Dr. Mercolaon the subject, he suggests you can avoid some of the improper drainage issues if you wear a bra that is properly fitted. Many, many women simply wear bras that do not fit. The website Linda's Bra School  offers plenty of guidance on proper bra fitting and can help you find a more appropriate bra style.