Recently, my own mother approached me with a personal medical question: “Is it true that I need to avoid antiperspirants given that I’m a breast cancer survivor?” From her tone, it was clear that she wanted a particular answer from me: “No, mom, that’s just a myth.” But in all honesty, I had no idea. Her surgeon had advised against antiperspirant use, but her radiologist denied any association between the product and breast cancer. So, in honor of my mother and her hopes of pursuing personal hygiene while being health-conscious, I began my search to answer the question: can antiperspirant cause breast cancer?
The upper outer quadrant (UOQ) of the breast exhibits the highest incidence of breast cancer. Multiple theories have been proposed to explain this disproportionate pattern of distribution. One theory is that the higher incidence of cancer in the UOQ is due to the greater amount of breast tissue in this area compared to the other quadrants . Other theories have focused on the proximity of the UOQ to the axilla, where underarm cosmetic deodorants are applied. Given the chronicity with which underarm deodorants are applied and the increase in use over the past decades, a link has been suggested between the active ingredients as well as the excipients, agents used to assist in delivery or stability, within these cosmetics, and the rising incidence of breast cancer [2, 3].
P-hydroxybenzoic acid esters (parabens) and aluminum salts, present within most cosmetic deodorants, are two compounds that have been investigated with regard to their role in breast cancer. Parabens are used in deodorants and multiple other cosmetic products for antimicrobial and preservative purposes, and studies have shown that these agents are readily absorbable through the skin.  In 2004, an article in the Journal of Applied Toxicology demonstrated evidence of parabens within breast tissue and breast tumors.  Moreover, early animal and yeast studies have suggested that parabens may have hormonal influences, with follow-up studies on human MCF7 breast cancer cells, one of the few and most commonly studied breast cancer cell lines, demonstrating that paraben esters have estrogenic activity [6-8]. With our knowledge of estrogen’s role in the development of certain breast cancers, one can further understand the role that paraben esters might also play given their proposed estrogenicity.
The role of aluminum salts—the main ingredient within antiperspirants—has also been studied. Aluminum salts are thought to prevent sweating by forming a physical plug of precipitated salts and damaged cells at the top of the sweat duct, thereby blocking escape of sweat from the skin’s surface. [9, 10] Studies have suggested that aluminum can alter DNA and cause epigenetic changes, both of which support its potential role in cancer development.  Moreover, breast biopsies have demonstrated aluminum levels within the breast tissue and the breast fat, with higher quantities seen in the outer regions of the breast.  However, another study published in 2013 demonstrated that aluminum concentrations did not differ in malignant breast tissue versus normal breast tissue. Additionally, the location of the tumor within the breast did not influence the aluminum concentration. 
Despite the multiple hypotheses regarding the link between parabens, aluminum salts, and breast cancer, well-designed studies demonstrating a direct, causal relationship are limited. Moreover, a handful of existing studies actually dispute any connection. For example, a population-based case-control study by Mirick et al. published in the Journal of the National Cancer Institute found no association between the use of underarm deodorants and breast cancer risk . Further analysis by type (deodorant or antiperspirant) and shaving practices failed to reveal any correlation. In 2008, a systemic review of the literature found no scientific evidence to support the studies’ proposed link between deodorant/antiperspirant and breast cancer, as many of the studies identified had flawed methodologies or did not directly answer the research question.  Additionally, a retrospective cohort study in Iraq interviewed 54 breast cancer patients and 50 control patients and found that 82% of controls used antiperspirants compared with 51.8% of breast cancer patients (P<0.05). 
Overall, while many studies indirectly link the excipients in antiperspirants to breast cancer, no studies convincingly prove a causal relationship. One possible limitation to these theories is that the amount of absorbed parabens and aluminum salts is not sufficient to cause the hormonal or genetic effects that would precipitate the development of breast cancer. Though there is some evidence supporting the carcinogenicity of parabens and aluminum salts, the amount and strength of evidence necessary to alter patient practices and recommend the discontinuation of underarm cosmetic deodorants is insufficient.
In conclusion, the question of whether deodorant or antiperspirant mediates breast cancer risk requires more research, as no casual link has been proved. Until more definitive evidence exists, it seems fair to allow women to make their own decisions about the use of underarm cosmetic deodorants.
So, what did I tell my own mother? Try to avoid deodorants or antiperspirants if feasible, because there may be a link that has yet to be unveiled, so why risk it? However, if antiperspirant deodorant is what you desire, no need to let the fear from an unproven connection hold you back. Go for it.
Dana Zalkin is a 4th year medical student at NYU School of Medicine
Peer reviewed by Susan Talbot, MD, Medicine, NYU Langone Medical Center
Image courtesy of Wikimedia Commons
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