Isopropyl myristate recommended for aimed rather than routine patch testing

Isopropyl myristate (IPM) is considered a very weak sensitizer. Patch test results with 20% IPM in petrolatum (pet.) in 8117 patients and 10% IPM in pet. in 4554 patients between January 1992 and December 2001 by the IVDK are presented. While irritant and questionable reactions were frequently observed, especially with 20% test concentration and 2-day patch test exposure, respectively, and a decrescendo pattern was common, morphologically positive reactions at day 3 were seen in only 16 patients, i.e. altogether 0.13%. In line with previous clinical and experimental evidence, our results indicate that IPM is an extremely weak sensitizer or possibly, in our material, not a sensitizer at all. IPM should thus not be tested routinely, but only in the case of suspected exposure as a possible source of allergic contact dermatitis, e.g. to cosmetics and perfumes, to avoid an unacceptable reduction of the positive predictive value of the test.