More than 40% wrongly thought that stress (43%) and food additives (42%) caused cancer, while one third incorrectly believed that electromagnetic frequencies (35%) and eating genetically modified food (34%) were risk factors.
Meanwhile 19% thought microwave ovens caused it and 15% said drinking from plastic bottles did too, despite a lack of good scientific evidence.
Among the proven causes of cancer, 88% of people correctly selected smoking, 80% picked passive smoking and 60% said sunburn.
Belief in mythical causes of cancer did not mean a person was more likely to have risky lifestyle habits. But those who had better knowledge of proven causes were more likely to avoid smoking.
Dr Samuel Smith, from the University of Leeds, said: “It’s worrying to see so many people endorse risk factors for which there is no convincing evidence.
“Compared to past research it appears the number of people believing in unproven causes of cancer has increased since the start of the century which could be a result of changes to how we access news and information through the internet and social media.
“It’s vital to improve public education about the causes of cancer if we want to help people make informed decisions about their lives and ensure they aren’t worrying unnecessarily.”
Dr Lion Shahab, from UCL, said: “People’s beliefs are so important because they have an impact on the lifestyle choices they make. Those with better awareness of proven causes of cancer were more likely not to smoke and to eat more fruit and vegetables.”
Clare Hyde from Cancer Research UK said: “Around four in 10 cancer cases could be prevented through lifestyle changes so it’s crucial we have the right information to help us separate the wheat from the chaff. Smoking, being overweight and overexposure to UV radiation from the sun and sunbeds are the biggest preventable causes of cancer.
“There is no guarantee against getting cancer but by knowing the biggest risk factors we can stack the odds in our favour to help reduce our individual risk of the disease, rather than wasting time worrying about fake news.”