The effect of long-term black tattoo on the skin of adult male guinea pigs and the probable role of imiquimod cream on tattoo removal: a histological and immunohistochemical study

Background:Tattoo is related to many skin problems, one of them being the necessity to remove it. Imiquimod is a novel synthetic compound with immunomodulatory action, and its role as a safe method to remove short-term tattoo within 7 days after tattooing was confirmed. Objective:The present study was conducted to investigate the effect of long-term (after 3 weeks) black tattoo on the skin of guinea pigs and the role of imiquimod cream in removing it. Methods:This study was carried out on 32 adult male guinea pigs. The animals were randomized and divided equally into four groups: group I (control group); group II (imiquimod cream group): animals in this group received topical application of imiquimod 5% cream once every 6 h for 7 days. Group III (tattoo group): animals in this group were tattooed once with black tattoo pigment. Group IV (tattoo/ imiquimod cream group): animals in this group were tattooed with black tattoo pigment, followed, after a gap of 3 weeks, by a topical application of imiquimod 5% cream on the tattooed skin once every 6 h for 7 days. At the end of the experiment, the animals were sacrificed, and specimens were taken from the skin of each animal. The specimens were subjected to different histological techniques and immunohistochemical stains for detecting macrophage Ab-1Mac 387. For statistical analysis, the slides were examined to assess the epidermal thickness, optical density of collagen fibers, and macrophage expression in the epidermis and the dermis. Results:The epidermis of the tattoo/imiquimod cream, the tattoo, and the imiquimod cream groups showed a significant increase in thickness compared with the control group. Keratinocytes showed cellular atypia, vaculation, pyknosis, and chromatin margination. The tattoo and the tattoo/imiquimod cream groups showed a significant increase in collagen fibers, whereas the cream group showed a significant decrease. Localization of tattoo pigments was seen in the tattoo/imiquimod cream group. Macrophage Ab-1Mac 387 expression in the skin of the tattoo/imiquimod cream and the imiquimod cream groups showed a significant increase compared with the tattoo group. Conclusion: Tattoo causes skin damage. Although imiquimod 5% cream alone caused localization of tattoo pigments and activation of macrophages, it has a hazardous side effect on the skin. Further studies should be conducted to find other ways to remove long-term tattoo with minimal side effects.