National Tattoo Day: The Photochemistry of Tattoos

National Tattoo Day is July 17th! Our runner-up to The 2023 SpectraWizard Spectroscopy Application Challenge had a fascinating application on the Photochemistry of Tattoos. The challenge starts back up next month, so get your applications ready and be on the look out for an update!

John Swierk, Ph.D.

Department of Chemistry | Binghamton University (SUNY)

Why does light cause a tattoo to fade? This simple question has huge implications as laser tattoo removal is a 4+ billion dollar a year industry. Surprisingly, despite the growing number of tattoos and laser removal we don’t actually understand how laser tattoo removal actually works. Our lab uses spectroscopy in lots of different ways to answer this question. One cool spectroscopy that we use is nanosecond shadowgraphy. Just like you can make shadow puppets with your fingers in front of a light, we use a nanosecond laser to illuminate a sample from behind. We can then zap the sample with another nanosecond laser and watch as an explosion and shockwave develops. From that we can figure out how hot and how much pressure the laser creates when it hits the tattoo. In order to perform nanosecond shadowgraphy, however, we need to be able to get light through the sample so we can’t use actual skin. Instead, we have developed transparent mimics of skin using polydimethylsiloxane (PDMS), a type of plastic, that mimic the mechanical properties of the different layers in skin.

Left: Nanosecond shadowgraph before. Middle: 124 nanosecond after a laser pulse. Black arrow points to shockwave from the laser strike. Right: Tattooed artificial skin made from multiple layers of PDMS that mimic the mechanical properties of the different skin layers.

We also use spectroscopy to understand what happens to tattooed skin that has been exposed to laser light. Working with a collaborator at Binghamton, we can tattoo skin from a cadaver and zap it with a laser. We can then slice the skin into thin slices and use X-ray fluorescence spectroscopy and Raman spectroscopy to understand what the tattoo pigments break down into and how much they move throughout the skin. We also use light to breakdown tattoo pigments in the lab and then use different spectroscopic techniques to figure out what the pigments break down into and whether those breakdown products are a risk to human health!