Background. Knowledge of cancer risk factors is unknown in Ireland. An understanding of risk factors could help inform cancer prevention programs.

Aims and Methods. A 48-question online survey was designed to gather data to assess levels of public knowledge about cancer risk factors.

Results. There were 748 participants (648 women, 100 men). Mean age was 37 years (range: 18-74 years). For the public, 81% were concerned about developing cancer; however, 20% believed that cancer is unavoidable if a family history exists, 27% believed that >50% of cancers are inherited, and 54% believed that 10%-20% of cancers are inherited; 20% were unaware that risk increases with age. The top five risk factors listed by respondents were smoking (87%), diet (76%), genetics (47%), alcohol (42%), and obesity (33%). Only 32% of the public were aware that obesity is a risk factor, and 33% did not think the location of fat was important. Moreover, 29% and 48% believed that risk could be increased by wearing a tight bra and by a blow to the breast, respectively. In addition, 85% and 86% believed that stress and that mobile phones, respectively, "strongly" increase risk; 12% believed that luck is important in avoiding cancer; 35% thought that "detox" diets could reduce risk; and 61% believed that organic food reduces risk. The majority were aware that physical activity of 30 minutes per day can reduce risk.

Conclusion. A sizable portion of the population is misinformed about cancer risk. Most participants were aware of classic risk factors (e.g., smoking, diet); however, many overestimated risk attributable to genetics, environment, and stress and underestimated age, obesity, and sunlight. One in seven participants believed that lifetime risk of cancer is not modifiable.