Tattooing has been practiced since thousands of years. The oldest tattooed skin ever discovered is the one of Ötzi the Iceman, dating around 3100 BC.

Tattoo ink consists of pigments (color) and a carrier (the liquid part).

The most common carriers are water, ethanol and glycerin.

Pigments derive from mineral sources.

Black, for example, is made by Mars Black, constituted by Fe₃O₄, the chemical compound of magnetite.

Red is made by Fe₂O₃, the chemical compound of hematite, commonly known as rust and commercialized as a pigment under the name of Pigment Red 101.

Yellow can be made using PbCrO₄, the mineral crocoite, called chrome yellow and a lot of other names, such as Paris yellow, Leipzig yellow and lemon yellow.

Nowadays, tattoos are very popular and scientists are trying to “use” them for medical purposes.

In 2008, Pokorna and collaborators published a paper suggesting the possibility of using tattoos for vaccination. DNA vaccination is a method of immunization in which a specific gene is introduced in our body. In this paper, the researchers compared the commonly used method, intramuscular injection, with the innovative one, tattooing. They demonstrated that tattooing technique stimulates the cellular immune response better than the traditional delivery method. Tattooing DNA vaccination is cheap, fast and induces a strong immune response and could be used for therapeutic purposes.

Recently, Yetisen and collaborators injected dermal tattoo biosensors to measure pH, glucose and albumin concentrations. These sensors change color when something not physiological happens to our body. For example, the sensor for the glucose concentration, changes from yellow to dark green when the glucose in our blood reaches pathological concentrations. These dermal tattoo biosensors are easy to inject, are safe and can be use in medical diagnostics to monitor diverse metabolites.

References:

Museum of Ötzi the Iceman website: http://www.iceman.it/en/

Helmenstine, “Tattoo ink chemistry”, (2019), https://www.thoughtco.com/tattoo-ink-chemistry-606170

Pokorna et al., “DNA-vaccination via tattooing induces stronger humoral and cellular immune responses than intramuscular delivery supported by molecular adjuvants”, (2008), https://doi.org/10.1186/1479-0556-6-4

Stuckey and Eilks, “Chemistry under Your Skin? Experiments with Tattoo Inks for Secondary School Chemistry Students”, (2014), https://doi.org/10.1021/ed400804s

Yetisen et al., “Dermal Tattoo Biosensors for Colorimetric Metabolite Detection”, (2019), https://doi.org/10.1002/anie.201904416