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Chromium is a metal that is widely used in several industries. It is also one of the most common metal allergens. Chromium is found in leather, cement, and other sources in the immediate household environment.
Both the trivalent and the hexavalent chromium ions are responsible for eliciting dermatitis at low concentrations. Hexavalent chromium can penetrate the skin unlike Cr(III), which makes it a more potent sensitizing agent.
The chromate (III) ion which is used in the tanning of leather has been identified in 95 percent of leather footwear products, at concentrations ranging from 0.3 to 3 percent, with a median content of 1.7 percent. Traces of chromate (VI) are also present, and are formed by the oxidation of chromium (III).
Chromium is also found in soil. However, concentrations of the chromate (VI) ion up to 450 ppm and of the chromate(III) ion up to 65,000 ppm are not considered to be risk factors for chromium-induced allergic contact dermatitis.
Household and detergent items also often contain chromium, but they are not considered to be a risk factor for chromium allergy, especially with the current industrial target of less than 5 ppm of chromium in such products.
Contact with such products is too brief, and levels too low, to allow significant sensitization to occur in such cases. The most likely cause of chromium allergy is contact with metal items such as jewelry, and with other objects in frequent or constant use. For instance, hexavalent chromium in metal screws and fittings has been shown to cause dermatitis in chromate-sensitive patients.
Repeated exposure to such objects around the house may cause persistent eczema of the hands.
Chromium allergy usually manifests as contact dermatitis, but may also have uncommon presentations. In sensitive individuals, chromium-containing metal prosthetic devices may cause pain, triggered by hypersensitivity to the corrosion products of the chromium.
Patients, who have, for instance, undergone total hip arthroplasty, may present with skin changes such as allergic contact dermatitis, delayed hypersensitivity type reactions resulting in eczema of the skin over the prosthesis site, and other late urticarial, bullous, or vasculitic reactions. In some cases, there is erythema multiforme, while others simply complain of tenderness accompanied by swelling.
The frequent occurrence of hip pain in patients who have undergone hip replacement may point to another long-term complication of chromium allergy, namely, loosening of the implant.
The mechanism of allergy in such cases is via a metal ion-induced activation of the immune system. The metal antigen is formed by the interaction between the metal corrosion products and various body compounds. These in turn stimulate T cells, leading to CD4 and CD8 activation and cytokine release.
The end result is a delayed-type hypersensitivity reaction which, in a high percentage of cases, leads to implant rejection. Males are more prone to chromium allergy, as are those who have occupational exposure to chromium.
The diagnosis of chromium allergy is based on the clinical history followed by special allergy tests. This includes patch testing, using a solution of 0.5% potassium dichromate in petrolatum, as dichromates contain Cr(VI). Patch testing is done with and without sodium lauryl sulfate, because the latter sharply reduces the elicitation threshold for sensitization.
Thus exposure to 5 ppmCr(VI) with 1% sodium lauryl sulfate (SLS), or 10 ppm of Cr(VI) alone, produces eczematous dermatitis, in chromium-sensitive patients. Interestingly, repeated open application testing, which is closer to real life, shows low correlation with patch test results.
Treatment consists of local measures to soothe the skin including emollients, corticosteroids to arrest and reduce the immune reaction, and treatment of secondary infection.
Cessation of exposure is necessary, but where this is absolutely not possible, other methods must be employed to prevent skin contact. These include the use of vinyl or rubber gloves and other protective clothing as desired, fixing wooden or rubber handles onto metal objects, or coating small objects with a few layers of clear nail polish.