Titanium is a light, strong, lustrous, corrosion-resistant (including resistance to sea water and chlorine) transition metal with a white-silvery-metallic color; in the periodic table it has the symbol Ti and atomic number 22. Titanium and its alloys are used for medical purpose like osteosynthesis, arthroplasty, pacemaker encasing, orthodontical wires, or in daily-use articles like spectacle frames. At a composition of 50% nickel and 50% titanium, the material nitinol can be folded but returns at given temperatures to its original form without damage. This shape memory effect is used for spectacle frames, flexible tubes, intravascular stents, or orthodontic wires. When exposing the latter to an acidic environment, a substantial nickel and titanium release can be observed. However, even 'pure' titanium materials used for implant alloys may contain nickel as result of the production process. Standard titanium alloys (TiAl6Nb7, TiAl6V4) and pure titanium discs supplied by five different titanium manufactures were shown to contain up to 0.034 wt % nickel, with iodide-titanium having the lowest percentage (0.002 wt %). Here, the nickel atoms are reported to be in solid solution in the titanium lattice. Suspected delayed-type hypersensitivity reactions to titanium were first reported as pacemaker dermatitis, but their existence is still put in question due to not always complete allergological work up and insufficient patch test preparations. In 1984, Peters et al. described a patient who had repeatedly cardiac pacemakers implanted and removed because pruritus, redness, and swelling of the skin overlying the pacemaker had developed within several weeks after insertion. These reactions were interpreted as contact sensitivity to the pure titanium encasing of the pacemaker, as there was a ++ patch test reaction to a thin square of metallic titanium applied with artificial sweat. Physiologically, it exists as an ion in the body. Humans exposed to titanium can develop pulmonary alveolar proteinosis (PAP, a disease of obscure cause that is characterized by the accumulation of a granular material that contains abundant lipid within the alveoli of lung.) with severe respiratory failure; analysis of particles found in lung tissues obtained by open lung biopsies demonstrated the presence of titanium. Salts of titanium are often considered to be relatively harmless but its chlorine compounds, such as TiCl2, TiCl3 and TiCl4, have unusual hazards. The dichloride takes the form of pyrophoric black crystals, and the tetrachloride is a volatile fuming liquid. All of titanium's chlorides are corrosive. (PMID: 7606971, 14756054, 16958916).