Leather

Most commercial leather is animal hide preserved by chrome tanning, which uses chromium(III) salts; under heat, light, or aging that chromium can oxidize into chromium(VI), the hexavalent form. Chromium VI is a potent skin sensitizer, which is why it sits at the center of leather's wearer-health story.

Chromium VI causes severe allergic contact dermatitis and can trigger it at very low concentrations, and chromium is the third most common metal allergy after nickel and cobalt, affecting roughly 1 to 3 percent of adults with a poor long-term prognosis. The hazard is real enough that the EU restricted chromium VI to under 3 mg/kg in skin-contact leather under REACH, a limit estimated to prevent about 80 percent of new chromium-related dermatitis cases. Studies have documented chromium VI releasing into artificial sweat from shoes in a real case of leather-induced dermatitis, so warm, sweaty contact, shoes, watch straps, waistbands, is where your exposure is highest.

Choose vegetable-tanned leather, which uses plant tannins instead of chromium salts, or look for OEKO-TEX Leather Standard or Leather Working Group certification, both of which test and cap chromium VI and other harmful residues.

Chrome tanning generates chromium-laden wastewater, while vegetable tanning cuts that toxic effluent by up to roughly 80 percent.