Cotton is one of the foremost crops grown for use in clothing production, but because it's not a food crop, pesticides, herbicides, and chemicals used on it are not regulated. In fact, 7 of the 15 pesticides that are regularly used have been labeled as "potential or known" carcinogens by the EPA.
Then, during the process of converting raw cotton into clothing, chemicals are added to the product. These include petroleum scours, softeners, brighteners, heavy metals, flame and soil retardants, ammonia and formaldehyde, just to name a few.
As an example, when cotton is spun into yarn, it receives a polyvinyl alcohol coating; this makes it easier to weave the fabric together.
Another example is the use of formaldehyde on baby clothes. The same chemical that was used to preserve things in your high school science class is often used as a finish on baby and adult clothes alike, as a preservative before shipping. That's one of the reasons that clothes stay looking so good on the store racks.
"That's fine," you might be saying, "I'll just stick to synthetic fibers." Not so fast, and here's why.