Candles, especially citrus ones, can lead to cancer because limonene, the substance that produces the citrus scent, is dangerous when it reacts in the air with ozone to create formaldehyde. That formaldehyde causes several cancers.

7 surprising things that can increase your risk of cancer

Most people know that carcinogens can cause cancer, but what is less ubiquitous are the various carcinogens that could be in household items, your food and in everyday items.

About 40 percent of men and women will be diagnosed with cancer, according to the National Cancer Institute. Most cancers are caused by genetic changes, because of aging and exposure to such environmental factors like tobacco smoke and radiation. Other controllable factors include what kind of food you eat, how much you eat and whether you exercise.

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What should be of relief to many is that some things thought to cause cancer don't, according to the National Cancer Institute. Those exemptions include antiperspirants, artificial sweeteners, bras, cell phones, charred meats, deodorants, flouride water, hair dye and power lines.

There are 250 unusual known carcinogens, according to lists of the National Toxicology Program and the International Agency for Research on Cancer. 

Here are 7 of the most surprising from the toxicology program’s list:

1. Air fresheners/scented candles

Reason for cancer: A substance used to give products that citrus smell, limonene itself is dangerous when it's released into the air and reacts with ozone because it creates formaldehyde. The National Cancer Institute has said formaldehyde is associated with several types of cancer.

 How to avoid them: Use fragrance-free cleaning agents. Also, reduce your use of scented products to reduce the amount of limonene and, therefore, formaldehyde exposure. Formaldehyde levels also can be reduced by using air conditioners and dehumidifiers.

2. Antioxidant dietary supplements

 Reason for cancer: Some studies have found that people who took antioxidant supplements during cancer therapy had worse outcomes, especially if they were smokers.

 How to avoid themAntioxidant supplements might need to be avoided or curtailed since some studies have shown an increased risk of some cancers. Check with your doctor before using any dietary supplement.

UNITED KINGDOM - NOVEMBER 27: By the 1920s links had been made between vitamins in foods and diseases, demonstrating the need for a balanced diet. Food supplements were developed to make it easier for people to get their essential vitamins and minerals. In recent years there has been debate about the benefits of taking food supplements. Vitamins A, C and E are thought to prevent a number of disorders including cancer and heart disease, and vitamin C is also taken to ward off colds. Vitamin D and calcium are believed to be essential in the formation of healthy skin and bones, while B vitamins and folic acid are thought to regulate mood and prevent depression and dementia. The manufacture of vitamins and food supplements is now a multi-million pound industry. (Photo by SSPL/Getty Images)
Photo: Science & Society Picture Library/SSPL via Getty Images

3. Calcium dietary supplements

 Reason for cancer: Calcium can reduce the risk of colorectal cancer but also may increase the risk of prostate cancer − both when taken in higher quantities. Since the evidence of potential benefit from calcium supplements is "limited and inconsistent," the National Cancer Institute does not recommend the use of calcium supplements to reduce the risk of colorectal cancer or any cancer.

 How to avoid it: Healthy people over 1 year old may safely eat foods containing calcium and take calcium supplements that together do not exceed 2.5 grams of calcium per day. However, too much of these calcium-rich foods − dairy products, dark green vegetables, some soy products, fish, nuts and legumes− can lead to kidney stones and even kidney failure.

4. Estrogen hormones

 Reason for cancerMenopausal hormone therapy (estrogen plus progestin, a synthetic version of the female hormone progesterone) can increase a woman's risk of breast cancer. That therapy, with estrogen alone, also can increase the risk of endometrial cancer.

 How to avoid them: Women should consult their doctors about estrogen therapy. Also, a protective factor against breast cancer is when women give birth, according to the National Cancer Institute.

Canned foods (stock photo).
Photo: Warren Price/Getty Images

5. Food packaging (like cans, plastics, Teflon)

 Reason for cancer: BPA linings in food and beverage cans are the danger, according to Breast Cancer Prevention Partners. Also, BPA and phthalates are a danger in plastics. The nonstick cookware of Teflon contains toxic compounds that have been linked to cancer.

 How to avoid them: Fresh or frozen items are better choices than canned foods. Also look for beverages, soups, sauces and tomato products in bottles or glass jars. Use glass, ceramic and stainless steel food storage containers and water bottles. 

6. Fragrance

Reason for cancer: It is legal for companies to use ingredients linked to cancer, endocrine disruption and reproductive harm in the cosmetics and personal care products.

 How to avoid them: Try to avoid any product that lists fragrance, parfum, phthalates, DEP, DBP or DEHP as an ingredient, according to the Breast Cancer Prevention Partners.

7. Being a transplant recipient

 Reason for cancerTransplant recipients are at increased risk of a large number of different cancers from the medications they are given to suppress their immune systems so their bodies won't reject the organs. These "immunosuppressive" drugs make the immune system less able to detect and destroy cancer cells or fight off infections that cause cancer.

 How to avoid them: Not as straightforward to prevent these. Some of these cancers may be contained, since they are caused by treatable infectious agents.

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