Contact allergy impurities

Coumarin is a component of cosmetics and fragrances for which conflicting results have been reported regarding its propensity to induce contact allergy. A careful study has shown that pure coumarin does not exhibit irritant or sensitizing properties. It only exhibits toxic properties when contaminated with impurities J43 ... 

Azathioprine, an immunosuppressant, is widely used in transplantation and autoimmune diseases cutaneous reactions to it are rare (Soni and Sherertz 1996). Two pharmaceutical workers have been described who had a contact allergy to azathioprine the role of impurities, such as mercatopurine and chloro-methylnitroimidazole, could not be elucidated (Burden and Beck 1992). 

Results from patch tests performed with impure preparations and with an insufficient number of controls for irritancy imply that some anecdotal reports on contact allergy to metals, such as antimony, iron, lead, silver, manganese, and zinc, may be questioned. Scientifically, as well as from a clinical point of view, it is somewhat challenging that nickel, chromium, and cobalt are so dominant, while the other metals in the periodic table of elements play such a minor role. 

Since cosmetic products come in thorough contact with various organs and tissues of the human body, a most important consideration for choosing ingredients to be used in these formulations is their medical safety. Many cosmetic preparations are left on the skin after application for indefinite periods. Therefore, the ingredients used must not cause any allergy, sensitization or irritation, and they must be free of any impurities that have toxic effects. 

Titanium salts used in various commercial products may lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin. However, the role of impurities cannot be ruled out for the incidence and severity of such allergies [230 ]. 

Bernard S, Baeck M, Tennstedt D, Haufroid V, Dekeuleneer V. Chromate or titanium allergy - the role of impurities Contact Dermatitis 2013 68(3) 191-2. 

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