Considering the amount of time you'll spend cozying up to your mattress, understanding the materials you're sleeping on is crucial. Unfortunately, mattresses have a bad reputation of being made with materials and chemicals, called volatile organic compounds (VOCs), that can cause health problems over significant periods of time. For example, foam can be made with petroleum oil, which can cause skin irritations, respiratory issues, and a plethora of other serious illnesses.
The problem is rooted in the lack of regulation and standardization in how mattresses are made. Manufacturers can use the words "natural" and "green" however they want, rendering these terms virtually meaningless. Truly organic mattresses have at least 95% certified organic fiber. Check the tag and fine print to see just how "natural" your mattress is before purchasing.
If you're looking for a guaranteed seal of approval, choose mattresses with a Global Organic Textiles Standard label, Global Organic Latex Standard label, or the Oeko-Tex Standard 100. These seals prohibit harmful chemicals and materials during manufacturing, and require that the product be tested for VOCs, among other things. You will, however, pay a significant premium for mattresses with these labels.