Azo Pigments in Tattoo Ink: Sunlight, Lasers and What Breaks Loose

Azo pigments give tattoo artists many of our bright reds, oranges and yellows. Their color depends on a chemical bond that can break under light or laser energy. I make and test ink, so I want to know which pigments are involved and what researchers have actually recovered after that breakdown.

What makes a pigment "azo"

An azo pigment has at least one azo bond: two nitrogen atoms double-bonded to each other (-N=N-), linking two ring-shaped aromatic structures. That linkage is what produces the color. Azo pigments are cheap to make, bright and fairly lightfast, which is why they dominate warm colors in tattoo ink.

Naphthol reds and diarylide yellows and oranges are two families artists are likely to encounter.

Naphthol reds include Pigment Red 22 and Pigment Red 170, both extracted from real tattoos. Diarylide yellows and oranges include Pigment Yellow 14 (CI 21095), Pigment Yellow 83 (CI 21108), Pigment Orange 13 (CI 21110) and Pigment Orange 34 (CI 21115). Those four are made by coupling onto 3,3'-dichlorobenzidine, which matters when looking at their breakdown products.

Not every warm color is azo. In breakdown testing reviewed by Hauri and Hohl, azo pigments in tattoo inks degraded easily under artificial sunlight, while quinacridones held up much better. That's why the CI numbers on the label matter.

What can break the azo bond

Light, laser irradiation and proposed enzymatic pathways need to be considered separately. They don't all have the same level of evidence.

Researchers dissolved Pigment Red 22 and exposed it to UVB or sunlight. The pigment clearly broke apart, nearly completely under sunlight. That was a solution experiment rather than tattooed skin, and the breakdown products pointed to cleavage at the azo bond.

Q-switched laser pulses deliver a different exposure. A 2018 study from Germany's Federal Institute for Risk Assessment (BfR) found that irradiating diarylide pigments released 3,3'-dichlorobenzidine, a known carcinogen. Tested separately, that compound caused DNA strand breaks in human skin cells.

Researchers have also discussed azo reductases, enzymes that can split azo colorants into aromatic amines. Their contribution to breakdown of tattoo pigment in living skin hasn't been established.

A 2021 systematic review of tattoo pigment breakdown products concluded that the limited research points to many possible toxic products from light-driven breakdown, including carcinogenic aromatic amines. The authors stressed how thin that research still is.

What happens in living skin

Your tattoo isn't static. In a mouse study tattooed with Pigment Red 22, about 32% of the pigment left the skin on its own within 42 days. Laser treatment cut the remaining amount by about 51%, and the researchers detected the corresponding hazardous aromatic amines in the skin. Thirty-two days under a solar simulator reduced the pigment by about 60%, which the authors also attributed partly to breakdown in the skin.

Those are mouse results. Nobody has measured how much of a human tattoo turns into amines over a lifetime of sun.

Why particle size matters here

A 2011 study of tattoo inks in general use found that most contained nanoparticles. Black pigments were made up almost entirely of them, white had the largest particles, and colors fell in between.

Smaller particles mean more surface area per drop of ink, and breakdown by light happens at the surface. Hauri and Hohl made the same point in their review: they assumed the finer particles in tattoo inks have more surface area than clumped pure pigment, which leads to faster breakdown reactions. Research on human tissue from BfR also found signs that smaller particles of an organic pigment were preferentially carried from the skin to the lymph nodes.

My personal thoughts: an azo pigment ground or sonicated finer than it needs to be may expose more of itself to UV and laser energy, and travel farther once it's broken loose. The surface-area part lines up with what Hauri and Hohl assumed. As far as I know, the full idea hasn't been tested directly in tattooed skin. I think it's one of the most important open questions in color ink, and it's a big reason I control particle size in my own inks.

What regulators have done

The EU's REACH rules for tattoo ink, in force since 2022, restrict listed carcinogenic aromatic amines and azo colorants that can release them. Swiss authorities had been testing inks for these amines for years before that, and found 3,3'-dichlorobenzidine in some samples. In the U.S., there's no equivalent limit yet.

What this means for artists and clients

Ask your supplier for the CI numbers of your warm colors, including whether a yellow or orange is a diarylide. Sun protection for a healed tattoo matters for pigment stability as well as visible fading.

Anyone planning removal should discuss the inks with their laser clinician, particularly reds and yellows. The breakdown products depend on the pigment and treatment conditions. REACH compliance offers another point of comparison when choosing ink, including for artists working outside Europe.

What we still need to know

Azo pigments aren't poison in the bottle, and a red tattoo isn't a health sentence. But the evidence is clear that light and laser energy can break some of them into compounds we wouldn't choose to put in skin. What's missing is human data on how much that happens and what it does over decades. Until we have it, I'd rather artists know the chemistry than guess.