Today, many of the bed sheets have chemicals in them, most notably formaldehyde. In general, all sheets made of polyester and cotton blends, along with anything permanent press or wrinkle-free, most likely contain formaldehyde. Using this chemical makes the bedding anti-wrinkle. But, it has been linked to cancer and respiratory illnesses, including asthma attacks. As a matter of fact, even small amounts of formaldehyde are hazardous to both health and the environment. It is recommended to go with a chemical free sheet.