The 'sparing phenomenon' of purpuric rash over tattooed skin.

Cutaneous complications associated with decorative tattooing are well known. However, the inhibition of a purpuric reaction by a tattoo is a fact that, as far as the authors know, has not been described before, fitting the definition of a 'sparing phenomenon', the absence of manifesting a particular skin disease in an area previously affected by another condition. From the clinical observation of purpuric lesions apparently inhibited by a tattoo in a 26-year-old patient, we performed an exact binomial test on the observed and expected proportion of purpuric lesions inside (0%, 95% confidence interval, CI, 0-2.6%) and outside (100%, 95% CI 97.4-100%) the tattooed skin, demonstrating a nonrandom distribution respecting the tattooed area (p < 0.001) and identifying the composition of the ink used in the tattoo (color pigment, glycerine, Hamamelis virginiana extract, water and alcohol). Moreover, we reviewed the cases of sparing phenomenon described in the literature. In conclusion this is the first report of a sparing phenomenon of purpuric lesions over tattooed skin.