Our products contain elements that come out of the ground, such as; chromium, molybdenum, and other minerals. The minerals themselves aren’t harmful and are essential to life. However, all minerals contain other compounds that require us to provide the warning of possible birth defects and cancer. The State of California requires such a warning for all products that are above levels that they choose, under something called a "Prop 65 warning (http://oehha.ca.gov/prop65/background/p65plain.html).
The State of California has identified more than 800 compounds that require this warning. This is not the same as a regulatory decision that a product is "safe" or "unsafe," it is a warning about specific ingredients – the list containing a wide range of naturally occurring and synthetic ingredients.