In recent years, tattoos have gained in popularity and have become a widespread expression of individuality. However, while many people appreciate the aesthetic side of tattoos, the question of possible health risks often remains unanswered. As part of the German National Cohort (NAKO), the Tattoo inK research project is investigating whether tattoos can increase the risk of cancer. On the occasion of World Tattoo Day on 21 March 2025, Dr Lena Koch-Gallenkamp, project manager of Tattoo inK (Abbreviation for „Tattoos in nationalen Kohorten“) and Dr Milena Foerster, Scientific Director of Tattoo inK, provide insights into the aims, methods and perspectives of this study. Koch-Gallenkamp is a scientist in the Department of Clinical Epidemiology and Ageing Research at the German Cancer Research Centre (DKFZ). Foerster works as an epidemiologist at the International Agency for Research on Cancer (IARC) in Lyon.
What would you like to find out about tattoo colours?
In general, we want to find out whether tattoos can cause cancer. Despite the great popularity of tattoos and their millennia-long history, very little is known about their potential long-term effects on health, which may come as a surprise to many people. Especially in light of the fact that toxicological analyses of tattoo inks, which are chemical mixtures of organic and inorganic colour pigments with various additives, have repeatedly identified carcinogenic and other dangerous substances.
“Despite the popularity of tattoos and their millennia-long history, very little is known about their potential long-term health effects, which may come as a surprise to many people.”
Dr. Lena Koch-Gallenkamp, Project manager Tattoo inK
During the tattooing process, these inks are injected intradermally, i.e. under the skin. The majority of the inks are transported to the local lymph nodes relatively quickly. Today, we assume that the pigment concentration in the lymph nodes concerned is around seven times higher than in the tattooed skin. As cancer primarily occurs where the concentration of carcinogenic substances is highest, lymphomas in particular, but of course also skin cancer, are of special interest.
“What exactly happens to the pigments in the lymph nodes is still unknown at present. However, it could lead to a chronic inflammatory reaction, which could favour the development of cancer.“
It is also possible that certain colours have an influence on possible long-term effects, as different chemical pigment classes occur more or less frequently in different colours. These could also interact with our bodies in a variety of ways due to their chemical structure and solubility. For example, other forms of cancer such as kidney or bladder cancer are also of interest for bright red, yellow or orange tattoos, as the corresponding pigments are more easily soluble and their degradation products could be metabolised and broken down by these organs.
“However, what we expressly cannot find out with our study is to what extent specific chemical substances could be responsible for the possible development of cancer. As tattoos are always mixtures of many different substances, such an investigation is not possible in epidemiological “real-life” studies.”
Dr. Milena Foerster, Scientific project manager Tattoo inK
What do we know so far about the health risks or side effects of tattoo colours?
Tattoos can have a number of side effects, but most of them are relatively rare. There are different types of side effects, on the one hand dermal complications, which are directly related to the tattoo pigments. These are, for example, granulomas, which can be visually perceived as thickenings or bulges in the tattooed skin and are caused by excessive pigment concentrations, usually in black tattoos. However, allergic reactions to certain substances contained in inks, which manifest themselves locally as painful ulcers or plaques on the tattooed skin, are associated with greater suffering for the tattooed person; such hypersensitivities can develop even years after the tattoo. Apart from such dermal reactions, there are infectious complications of a bacterial or viral nature, which can be caused by poor hygiene during the tattooing process or aftercare. While bacterial infections manifest themselves immediately, viral infections such as hepatitis C can remain undetected for years and have serious long-term consequences. The frequency of such complications is unfortunately very uncertain, but viral infections are certainly very rare nowadays.
How is the information collected for the Tattoo inK project and what methods do you use to find out how the tattoo colours could affect health?
“The information within the German National Cohort (NAKO) is collected by questionnaire, either online or on paper. The questionnaire, which is also being used in a population study in France, consists of around 30 questions on visual factors such as the area or colours of the tattoo, contextual factors such as when, under what circumstances and in which country the tattoos were engraved, as well as questions on undesirable side effects, sun exposure and tattoo removal.”
The data from the study will be analysed statistically on a longitudinal basis by comparing the tattooed and non-tattooed NAKO participants with regard to the occurrence of future cancers. The research into these correlations observed the health progression of the participants over many years, so the analyses and findings will take some time. However, we will certainly be looking at the cross-sectional data by then. Here, for example, we will be able to make statements about the frequency of side effects caused by the tattoos among the people surveyed.
Are there already initial results from the NAKO or from the partner study of the French population study Constance, which is currently carrying out a similar project?
There are currently no results from NAKO itself, as the collection of tattoo data has only just been completed. Currently, more than 8000 online questionnaires have been completed. The paper questionnaires are currently being counted. A total of around 13,000 participants from 16 study centres are planned to take part in the Tattoo Ink project. The data from the paper questionnaires are still being entered before they are ready to be analysed.
The partner study in France is already a little further along. Initial analyses of the data have highlighted the hepatitis C risk. In the study, it was almost five times as high in test subjects who did not get tattooed in tattoo studios compared to those who were tattooed in studios or were not tattooed at all. This finding is also important because hepatitis C infections themselves increase the risk of lymphoma and this correlation must therefore also be taken into account in corresponding subsequent analyses.
“Initial analyses of the data [from the French population study Constance] have made the hepatitis C risk clear. In the study, it was almost five times as high in subjects who did not get tattooed in tattoo studios compared to those who were tattooed in studios or were not tattooed at all.”
What role does the World Health Organisation (WHO) play in the project?
The German Cancer Research Centre (DKFZ) in Heidelberg is leading the study in collaboration with the International Agency for Research on Cancer (IARC) in Lyon, which is part of the WHO. The cooperation with the IARC/WHO has the advantage that any results can very quickly lead to the development and implementation of necessary prevention programmes, including at international level.
Who can take part in the Tatoo ink study?
Participation in Tattoo inK is open to all NAKO participants who have or have had at least one tattoo. Participation is of course voluntary.