This is the category that holds the majority of the skin-harming culprits. Man-made fabrics like acrylic, polyester, rayon, acetate, and nylon are treated with thousands of harmful toxic chemicals during production, according to ScienceDaily. In a study from Stockholm University, researchers chose four groups of substances related to health risks and tested them for “occurrence, quantity, toxicity, and how easily they may penetrate the skin,” and the highest concentrations of two of the substances were found in none other than polyester.

Toxic chemicals aside, synthetic fabrics simply don’t breathe, and anyone who’s worn polyester on a hot summer day is probably well aware of that. The fabric also traps odors, which Popular Science explained in an article. Not to go into too much gory detail, but skin germs found in sweat feast on chemicals, which synthetic fibers can’t absorb, therefore creating an environment for smelly bacteria to grow. All signs point to polyester being the number one worst fabric for skin.