Eruptive milia and acneiform hyperkeratosis with comedones (pseudo-epidermal cysts) within tattoos

Milia are small, hard, white superficial epidermal cysts measuring a few millimetres that can occur during skin healing due to occlusion of pilosebaceous units. Milia rarely occur on tattoos. However, cases of allergic reactions with hyperkeratosis and open comedones have been described in the literature, sometimes under the term "epidermal cysts".

We saw three patients who developed milia, including a 32-year-old man with eruptive milia 10 weeks after getting a black, red and green tattoo on his upper arm. Topical tretinoin was applied. We encountered two further cases of eruptive milia on black/grey tattoos. A fourth patient presented a massive hyperkeratotic reaction with retention comedones on the red/pink area of a tattoo.

The occurrence of milia and acneiform allergic reactions after tattooing is rare. We collated a total of 13 cases from the literature, of which 8 involved milia. This condition occurred within 3 months following tattooing, with no particular correlation with any given colour, and generally without any allergic reaction (except in one case). Reactions comprising excessive acneiform hyperkeratosis and open comedones were noted with pink and red inks and were a complication in a setting of allergic inflammatory reaction. However, the histopathology of these reactions is poorly described in the literature. It seems inappropriate to diagnose the condition as "epidermal cysts" since the lesions are not in fact simple cysts but rather retention lesions occurring during an inflammatory reaction and are thus different from post-traumatic milia.