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.

2. Antioxidant dietary supplements

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

4. Estrogen hormones

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

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

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.

7. Being a transplant recipient

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