Memory foam, also called visco-elastic foam, is made of conventional polyurethane foam that has been restructured on a molecular level by adding a complex formulation of chemicals. Those who are allergic to polyurethane will probably be allergic to memory foam.
Memory foam is designed to react to body temperature, which is how it molds itself around the sleeper. According to Allergy Consumer Review.com, some claim that when the memory foam heats up, it emits trace vapors that can provoke allergic reactions. There have been no objective studies to confirm this.
There are hundreds formulations of memory foam used by manufacturers. If an allergy sufferer has a reaction to one memory foam product and not another, it is probably due to a sensitivity to one of the chemical additives.
Some memory foam products are layered with other material. Adhesives used in the construction of layered products could be the source of an allergic reaction.
Memory foam resists dust mites, a common allergen.