There's a company out there you may be familiar with (once again, I'll keep their name to myself). Their main focus is creating products with ingredients that score low in the EWG Cosmetics Database. They make a lot of color cosmetics and have gone to admirable lengths to ensure that the levels of naturally-occurring lead in their products is at the lowest level possible. (Lead, a naturally-occurring heavy metal in the earth's crust, can be found in trace amounts in mineral ingredients used to create colors in makeups because it's inherently found in the ground.)
However, while they're concerned about lead, they intentionally add other concerning metals to their products, with one lipstick containing: tin oxide, Yellow 5 Lake, Red 5 Lake, Red 7 Lake, Red 27 Lake, and Blue 1 Lake. (Of course, there are lots of other companies that use these colorants, but this company's main marketing point is safety, so I'm bringing it to the table today.)
First of all, there's hidden aluminum in this product. Yellow 5 Lake, Red 5 Lake, etc, are all artificial colors made from coal tar and--you guessed it: aluminum.
While most of these artificial colors score low in the Cosmetics Database (due to lack of data) there are inherent problems with these colorants. First of all, they contain aluminum (read more about the harmful effects of aluminum here.) Tartrazine (yellow 5 lake) was recently found to be a xenoestrogen in a lab study on human breast cancer cells. (Source) (Not surprising since aluminum is a metalloestrogen.) Yellow 5 Lake has also been found to create free radical damage to DNA in the colon in several animal studies. (Source).
Another problem ingredient is tin oxide. The affects of tin on the human body are still largely unknown. (source) While some sources say it is quickly removed from the body after ingestion, traces are known to remain in the body. Tin is not an essential mineral with any positive biological function and can have adverse effects. First of all it is known to create free radical species (damage) to cells. Some tin compounds can have neurotoxic effects (although it's generally considered that tin oxide does not.) (source) Tin is also suspected to replace calcium in bone, possibly leading to osteoporosis.
"In one study, rats were fed tin at concentrations of 10, 50, 100, or 250 parts per million in the diet. At tin concentrations of 50 ppm or greater, blood levels of calcium were reduced and the calcium content of certain areas of femur bone was diminished." (source)
An ingredient listed on a product would have much higher levels of tin than would be measured in parts per million. (Usually around 1% of the formula.) And while tin oxide is approved as a safe ingredient by the Cosmetics Ingredient Review, they assessed its safety based on the fact that it's not absorbed easily through the skin. However, the safety of tin oxide in a lipstick product with potential for ingestion was not assessed in particular. (Source.)
So, while this company has done a great job of working to avoid lead and other heavy metals, we can't forget about the potential harmful effects of other metals intentionally added to the product.
The takeaway: no matter what, always read your ingredients!