Some deodorants have some toxic ingredients like aluminum, parabens, propylene glycol, phthalates, antriclosan.
Aluminum-containing underarm antiperspirants that are left on the skin near the breast. Since it's left on the skin, the skin later absorbs it causing the skin to have estrogen. Estrogen is a type of hormone made by the body it helps develop and maintain a females characteristics and the growth of bones. Estrogen can also be used as a type of birth control for menopause, menstrual disorders, osteoporosis, and other conditions.Estrogen can cause the growth of cancer cells, the components of aluminum have some based compounds that might be causing the development of cancer. Some studies are saying aluminum is having direct contact with breast tissue.
A few studies have been made to determined if deodorant is actually causing cancer. But they haven't actually found real evidence.
Links:
https://www.cancer.org/cancer/cancer-causes/antiperspirants-and-breast-cancer-risk.html
http://www.webmd.com/skin-problems-and-treatments/features/antiperspirant-facts-safety#1
http://time.com/3922814/deodorant-cancer/
