Six Classes

Six Classes is a framework developed by the Green Science Policy Institute to provide information about many  of the harmful chemicals used in building materials and consumer products, in order to minimize their use. Rather than creating a list of chemicals of concern, Six Classes groups chemicals into six categories. This strategy was introduced because the huge quantity of chemicals used in the United States (over 80,000) has made studying them one at a time a significant challenge. As a result, many have not been studied sufficiently, and their effects on human health and the environment are not fully understood. Six Classes was also created to address a common problem when harmful chemicals are eventually removed from circulation – their replacements are often “chemical cousins,” or closely-related substances with similar risks. By grouping substances with similar structure, use, or properties, manufacturers can avoid such “regrettable substitutions” and move towards truly safer replacements. Manufacturers, retailers, designers, and large purchasers can use this approach to evaluate chemicals used in their products, and perhaps sometimes even choose to phase out entire classes of chemicals.

The Six Classes include many commonly used chemicals of concern that are known to degrade, evaporate, or otherwise escape from products and cause harm to humans, wildlife, and the environment:

  • Per- and polyfluoroalkyl substances (PFAS) are found in products from textiles and food packaging to adhesives and sealants. They can remain in the environment forever and are linked to serious health issues.
  • Antimicrobials can be found in many building materials, furnishings, cleaning, and personal care products. Many are associated with developmental, hormonal, respiratory, and reproductive problems, and cause widespread contamination of the environment and wildlife.
  • Flame retardants are often not effective at improving fire safety and are detrimental to health and the environment.
  • Bisphenols and phthalates are found in many plastics to improve flexibility. They can alter hormones and disrupt vital body systems even at very low levels of exposure.
  • Some solvents used in adhesives, paint strippers, and aerosols, are associated with neurological issues and increased risk of cancer.
  • Certain metals such as mercury, arsenic, cadmium, and lead, are harmful to human health, with particular risk for fetuses and young children. In the environment they do not break down and accumulate in ecosystems.

The Green Science Policy Institute’s mission is to facilitate safer use of chemicals to protect human and ecological health. We educate and build partnerships among government, business, academia, and public interest groups to develop innovative solutions for reducing harmful chemicals in products.1 Learn more on their websites:,, and

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