Tattooing: immediate and long-term adverse reactions and complications.

Tattooing has become a popular global trend in industrialised countries, with the highest prevalence rates of up to 30-40 % in the adult population younger than 40 years. Common tattoo inks may contain heavy metals, polycyclic aromatic hydrocarbons, and primary aromatic amines, toxic if exceeding permissible limits. It is estimated that about 14.36 mg of ink is injected per cm² of skin, at a depth of 1-3 mm. The injected pigment is internalised by neutrophils, fibroblasts, and macrophages or dendritic cells. About 60-90 % of the pigment is then transported to the lymph nodes via the lymphatic system and to other organs, such as the liver, spleen, and lung, through blood. Adverse reactions can be immediate (irritation, infection, inflammation of the skin), delayed (hypersensitivity reactions), and can result in long-term complications (fibrosis, granulomatous changes, systemic inflammation, and sometimes malignant diseases such as lymphoma). Pigments in tattooed skin can be identified by skin biopsy, chemical imaging, and histochemical and immunohistochemical analyses. Harmful effects of tattoo inks have been investigated ex vivo, in vitro, in vivo, and recently in silico. Studies in humans mainly refer to case reports, but there are no epidemiological studies that would evaluate the potential links between tattoos and cancer or other disorders. As the safety of people getting tattoos primarily depends on the quality of tattooing products, it is necessary to create a general regulatory framework.