Fluoride is in your drinking water and in your toothpaste to help fight tooth decay.
But armed with studies that conclude fluoride can cause osteosarcoma, a form of bone cancer, concerned groups asked the state to list it as a carcinogen.
The Office of Environmental Health Hazard Assessment debated whether fluoride belongs on the Proposition 65 list.
California voters passed Proposition 65 in 1986. It's a warning label that the business you're visiting or product you're using could expose you to cancer-causing substances.
While municipalities would have been exempt from telling you the fluoride in your tap water could cause cancer, toothpaste makers would have had to add a Prop. 65 warning label on the box or tube.
Dentists were worried because it could scare people into not brushing their teeth.
"We want to reduce the amount of tooth decay, and we've done a fantastic job in reducing tooth decay, such that half the children now in the United States don't have any tooth decay at all," said Howard Pollick, a dental professor at the University of California San Francisco.
But scientists urged the panel not to dismiss the studies, especially the results in children.
"Exposure to fluoride in tap water during the mid-childhood growth spurt ages 5 to 10 is linked to higher levels of osteosarcoma in males age 10 to 19," said Rebecca Sutton, an Environmental Working Group senior scientist.
In the end, the panel unanimously voted against warning labels on toothpaste because the studies overall were inconclusive.
Public health officials praised the move.
"The science is very clear and very definitive. This is a safe and effective tool to prevent dental decay and it in no way has any ill effects on any individual's health," said Catherine Hayes, American Association of Public Health Dentistry.
More than 800 chemicals are on the state's Prop. 65 carcinogen list.
Fluoride will not be added.