A failure-to-warn claim is a staple of products liability litigation. The basic premise is that a manufacturer or seller failed to warn a consumer about an unreasonable risk of foreseeable harm associated with the use of a product.

Plaintiffs pursuing toxic tort cases have begun to rely on failure-to-warn claims outside the strict consumer/seller context. Specifically, several personal injury lawsuits relating to the emerging contaminant per- and polyfluoroalkyl substances (PFAS) have relied on failure-to-warn theories against manufacturers of PFAS. These lawsuits are distinct from many failure-to-warn cases in that the plaintiff is rarely a user or purchaser of the PFAS-containing product. Rather, the plaintiff is a mere bystander who, because of the conduct of the user of the product (the one the manufacturer allegedly failed to warn), was exposed to PFAS chemicals.