Being on your phone
Phones aren't chemicals, so they're not on the official Prop 65 list, but the California Department of Health still warns that the radio frequency energy they emit might cause cancer.
Scientific studies haven't demonstrated that cellphone radiation levels are anything to worry about in humans, though researchers have noticed some worrisome tumor growth and heart-tissue damage in rats who were exposed to cellphone radio frequency radiation, Science Friday recently reported, though the scientists weren't able to replicate the effects in mice.
California residents are told to not keep their phones in their pockets and to store them away from their bed at night. The health department also suggests people use wired headphones, wireless headsets, and speakerphone capabilities instead of holding their phone up to their ear, and send more texts to avoid keeping phones close to their heads.
Staying at a hotel
Even spending a little time as a tourist in California can increase your cancer risk, the state says.
"When you check in at a hotel, look for a Proposition 65 warning sign at the hotel's check-in desk, or a warning printed on the registration form," the state says, adding, "If you have any questions about the warning, ask hotel representatives."
Not all hotels have the cancer warnings — much of the danger California is worried about in hotels comes from toxins in substances like secondhand smoke or alcohol.
Drinking and smoking are both activities known to increase your risk of developing cancer, so California suggests choosing smoke-free hotels or avoiding smoking areas.