Thanks to scientists working under the auspices of the World Health Organization, you can be fairly sure your toothbrush won't give you cancer. Over four decades, a WHO research agency has assessed 989 substances and activities, ranging from arsenic to hair dressing. It found only one that was "probably not" likely to cause cancer: an ingredient in nylon that is used in yoga pants and toothbrush bristles.
All the other 988 substances, however, pose some level of risk or need further research, according to the International Agency for Research on Cancer (IARC), an arm of the WHO. Some things in the IARC's top category of carcinogens are pretty obvious nasties, such as plutonium, mustard gas and tobacco. Others are more surprising: Also ranked as "Group 1 carcinogens" are wood dust and Chinese salted fish.
The IARC has said that working as a painter causes cancer, using a mobile phone possibly does and working shifts as a pilot or a nurse, for example, is "probably carcinogenic."