Chromium exists in every one of the oxidation states from -(II) to +(VI), but only the valencies of (0), (II), (III) and (VI) are common. Only the trivalent and hexavalent salts are sufficiently stable to act as haptens, therefore able to form covalent bonds with proteins(1, 2) and cause allergy. This protein-binding capacity is the general precondition of immunogenic activity of a hapten, already shown 60 years ago(3).
It is generally accepted that chromium metal itself does not act as a hapten and is accordingly non-sensitising(1, 2). Theoretically, sweat or plasma could transform metallic chromium into allergenic chromium salts. Saliva could have a similar action on chromium-containing intraoral devices. Chromium released from household utensils could also transform into chromium salts. Accordingly, ingestion of chromium compounds may induce systemic contact dermatitis (see below). Data on the above aspects are anecdotal. Some aspects of chromium allergy in relation to the skin are reviewed in this article.