Cell phones, stress, and genetically modified foods. Of these, which causes cancer? The answer: none. Contrary to popular belief, there’s no scientific evidence that any of these things increase the risk of cancer. But, just as some things seem like they would cause cancer but don’t, there are other things that don’t seem like carcinogens but are. 

Here’s a closer look at seven unusual, but scientifically studied, risk factors for cancer.

Scented candles

What could be more peaceful and relaxing than a scented candle? Hold on, don’t get too relaxed. The evidence is mounting that burning scented candles may result in cancer, particularly bladder cancer.

Though they seem perfectly harmless, scented candles burned indoors can release a large number of volatile organic compounds known to be bladder carcinogens. In one investigation, researchers found a total of 34 compounds released from burning scented candles, including a high abundance of potentially carcinogenic formaldehyde as well as aromatic hydrocarbons such as toluene and benzopyrene.

“Scented candles, widely used for relaxation purposes, may emit plenty of biologically active substances that are inhaled and gradually accumulate in urine, analogously to compounds found within tobacco smoke,” wrote the authors of a recent review article. “We should be concerned about the unrecognized sources of potentially carcinogenic chemicals that may be present in our households.”

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Oral sex

Mention of the human papilloma virus (HPV) likely makes you think of cervical cancer. However, the most frequently diagnosed HPV-associated cancer type is no longer cervical cancer but oropharyngeal cancer. And, HPV-related oropharyngeal cancer is strongly linked to oral sex.  

The greatest risk for contracting oral HPV and developing HPV-related throat cancer is having multiple oral sex partners, warned Brandon Prendes, MD, head and neck surgeon at the Cleveland Clinic, Cleveland, OH.

HPV-related throat cancer can take up to 30 years to appear, so it’s most common in adults between the ages of 40 and 60.

Dr. Prendes said:

“I don’t think anyone in our field or any epidemiologist would argue the link between HPV and throat cancer at this point.” “It’s a strong link.”

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Frequent flying

In several studies, researchers have shown an association between frequent flying and increased cancer risk. In a 2014 study in which researchers compared the health of US flight attendants with the general population, they found that female flight attendants reported 34% more reproductive cancers. 

These findings were supported by those from a 2018 cross sectional study of flight attendant health. In this study, researchers observed higher rates of female reproductive cancers and cancer at all sites among females compared with the general population. 

In yet another study, in which researchers characterized the prevalence of cancer diagnoses among US cabin crew compared with the general population, flight attendants were shown to have a higher prevalence of every cancer assessed—especially breast, melanoma, and non-melanoma skin cancers. 

Some researchers have suggested that these excess cancer risks may be due to occupational exposures to ionizing radiation of cosmic origin, as well increased sun exposure. 

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Breast implants

Breast implants were introduced in the 1960s, and ever since that time, experts have raised health concerns about them. In fact, between 1992 and 2006, silicone-gel implants were temporarily banned in the United States. 

Nonetheless, no significant correlations between silicone breast implants and autoimmune diseases, cancer, and connective tissue disease were elucidated until 2008. In an epidemiological study published in JAMA, researchers demonstrated an increased risk of breast-anaplastic large-cell lymphoma (ALCL) in association with breast implants, based on five cases. By 2018, the number of breast-ALCL cases cited in the literature rose to 173 cases. As a result of these discoveries, breast-ALCL has been included as a novel disease entity in the WHO’s classification of lymphoma.

In a follow-up, population-based study published in JAMA Oncology in 2018, researchers uncovered 32 cases of breast-ALCL due to ipsilateral implants and suggested the following underlying etiologies:

“A local inflammatory response, elicited by silicone-derived products or specific bacterial species adherent to the prosthesis surface (biofilm) may play a role, possibly via an auto-immune response. Toxic products related to the production of breast implants have been implicated as direct mutagens. Whether certain groups of women have a genetically determined increased risk to develop lymphoma when exposed to breast implants, eg, via a genetically determined altered or exaggerated local immunological response, remains hypothetical.”

The researchers estimated that the relative risk for breast-ALCL in women with breast implants was 421.8. They also estimated that the absolute cumulative risk was 29 per million among women aged 50 years and 82 per million among women aged 70 years. Suffice to say, although possible, the risk of cancer due to breast implants is low.

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Piping hot beverages

In the Middle East, China, and other parts of Asia, piping hot tea is a favorite. But, burning-hot water hitting the esophagus can be bad for business. Specifically, it can cause metaplasia, which can progress to cancer.

To be sure, the suggestion that copious cups of hot tea can result in esophageal cancer is an old one. Back in the 1930s, New York physician Dr. W. L. Watson hypothesized that the cases of esophageal cancer he observed in Russian-born patients were samovar related.

“Thermal irritation is probably the most constant factor predisposing to the cancer of the esophagus. The drinking of copious amounts of excessively hot tea is a history frequently obtained from Russian-born patients coming to Memorial Hospital suffering from cancer of the esophagus,” wrote Dr. Watson.

In 2016, the International Agency for Research on Cancer classified drinking extremely hot beverages as a probable—but not definite—cause of cancer. An expanding corpus of research supports very hot tea and other scalding beverages as a possible carcinogen.

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Alcohol consumption

Next time you raise a glass in a toast to health, keep in mind that any level of alcohol consumption—light, moderate, or heavy—is linked to cancer, at least according to the American Society of Clinical Oncology (ASCO).

“People typically don’t associate drinking beer, wine, and hard liquor with increasing their risk of developing cancer in their lifetimes,” said ASCO President Bruce Johnson, MD, in a statement. “However, the link between increased alcohol consumption and cancer has been firmly established and gives the medical community guidance on how to help their patients reduce their risk of cancer.”

We all know that alcoholic cirrhosis results in hepatocellular cancer. But any alcohol intake is tied to other types of cancer, including breast, colon, esophagus, and head/neck. Between 5% and 6% of global cancer deaths are secondary to alcohol. Nevertheless, per ASCO survey results, 70% of Americans don’t recognize alcohol as a carcinogen. Yikes!

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Lack of sunlight

Vitamin D deficiency has evolved into a full-blown pandemic. People fail to recognize that moderate sun exposure is the best way to produce vitamin D, which is rarely found in foods. Even foods that are fortified with vitamin D lack sufficient levels for adults and children. Vitamin D deficiency has not only been linked to a number of common cancer types, but also to autoimmune diseases, hypertension, and infectious diseases.

This story is contributed by Naveed Saleh and is a part of our Global Content Initiative, where we feature selected stories from our Global network which we believe would be most useful and informative to our doctor members.