Millions of man-made chemicals have been described in scientific literature since the late 19th century. Production continues apace: something like 6,000 new chemicals are added to the list every week and at least 70,000 are currently in production. Only a fraction of this toxic load has been adequately tested for the long-term effects on human health.
We meet chemicals in the air, our food, water supplies and by direct contact. Medical drugs add their share, and even the clothes we wear and the fabric of our homes are mostly artificially made, needing many complex chemical precursors which linger on the final product. Some of these fabrics emit toxins long after being installed in the home. It is a fact of life in the modern world that indoor pollution can be just as bad, or worse, than the outdoor kind.