Polyester resins are one of the largest classes of synthetic resins and are used extensively in the reinforced plastics industry and in water-based paints, powder coatings, lacquers, automotive cements, and glues. Allergic contact dermatitis from polyester resins is rare. When allergic contact dermatitis does occur, it is more often from ancillary components of the resin system, such as accelerators, catalysts, and inhibitors, than the resins themselves. The small amount of allergic contact dermatitis that does occur from polyester resins is mostly due to unsaturated polyester resins and extremely rarely from saturated polyester resins. Occasionally, allergic contact dermatitis may result from monomers liberated from the hardened resin or its dust. Irritant contact dermatitis from polyester resin systems occurs more frequently than allergic contact dermatitis. Irritant contact dermatitis and chemical burns may occur from additives such as organic peroxides, styrene, and acetone. Contact urticaria is well known to occur from acid anhydrides.