In 1986, California voters approved an initiative called the Safe Drinking Water and Toxic Enforcement Act due to their concerns of overexposure to toxins. This act is now known as Proposition 65. The state law only applies to California (or any products shipped/sold to California). Propsition 65 requires the state to publish two lists of chemicals: one list of chemicals known to cause cancer and another list known to cause birth defects or other reproductive harm. The state updates these lists once a year. Now, the list has grown to include well over 950 chemicals since it was published in 1987.
Proposition 65 warnings can be found all over California, including restaurants, amusement parks (including Disney Land), work environments, parking lots, hospitals, rental properties and dental offices. You can find the warning label on many consumer products, including products that are 100% natural and have been certified organic.
The list includes all chemicals shown to be a reproductive toxin or carcinogen in laboratory animals. Proposition 65 even includes chemicals that have not been tested on humans or occur naturally in very low quantities (such as lead, which is in soil).
You can find more about Proposition 65 on California’s OEHHA website.