A Brief History

Tattooing has been a part of many cultures for thousands of years. It is now estimated that almost a quarter of the United States college-aged population has one or more tattoos (1). For many years tattoo inks contained metals such as cadmium, cobalt, mercury and lead (2).  In 1976 the Food, Drug and Cosmetic Act was passed which limited allowable concentrations of lead and mercury in tattoo inks; similar laws have been passed in other countries (1,2). However, the metal content in tattoo ink pigments remains highly unregulated.

The Two Metal Rainbows

Metals have been used in tattoo inks because of their properties as color pigments. Commonly used metals include titanium dioxide (white), mercury (red), iron (black, brown), cadmium (yellow) and copper (blue, green) (2,3).  However, in their reduced states the pigmentation of these metals changes. Ferric oxide, a brown-red colour, can be reduced to ferrous oxide which is black (3). White titanium dioxide (Ti4+) turns blue when reduced to Ti3+ (3). Yellow ink containing cadmium has been shown to turn black, as do copper and mercury containing pigments (6).

Q-Switched Laser Removal of Tattoos

Of tattooed persons, reports estimated that 10% will request removal of their tattoo (5). The most commonly used way to accomplish this is treatment with quality switched (Q-switched) lasers. Q-switched lasers use thermal destruction of specific targets to remove pigmentation (1). This occurs by targeting selectively absorbed wavelengths at a pulse duration shorter than thermal relaxation time (the time it takes for the pigment to cool down to half the temperature to which it was heated) (1). In essence, the wavelength of the laser is matched to the wavelength of absorption of the pigment (6). The three main kinds of Q-switched laser are: Q-switched Nd:YAG for black, blue, red, yellow and orange pigments, Q-switched ruby for black, blue-black, green and blue pigments and Q-switched Alexandrite for black, blue and green pigments (1,6).

tattoo removal

Proposed Mechanism

When the laser light is absorbed by the pigment molecule, the light energy is converted to heat or to break chemical bonds in the pigment molecules (6). As the pigment heats up, the pigment molecule becomes extremely hot and causes rapid expansion of the water surrounding the molecule within the cell (6). This in turn creates negative pressure and a shock wave is created near the surface of the pigment molecule which helps to destroy it (6). The newly created smaller fragments are released into the lymphatic system and removed from the body (6).


Unfortunately, laser treatment does not always result in removal of pigment and a darkening of the tattoo can occur. A large offender in this practice is titanium dioxide. Since titanium dioxide manifests as a white pigment it is often combined with other inks to lighten them and has been found at concentrations of up to 40% in many inks (3). When laser treatment is applied, titanium dioxide is reduced and turns dark black, resulting in a darkening of the tattoo (3). Ultrastructural (electron microscopy) studies show that in tattoos that darken, the pigmentation particles in the darkened regions are much smaller than those in untreated regions and more loosely distributed than pigmentation particles of tattoos that had lightened (3). The exact mechanism by which the darkening occurs is not known (6). 

tattoo particles tem

Image taken from Ross, EV (Reference 3). Arrows in B point to smaller, fragmented pigment molecules while C shows deeper tissue layer with untreated, unfragmented particles.


(1) Pfirrmann, G., Karsai, S., Hammes, S., Raulin, C. Tattoo Removal- State Of The Art. Journal of the German Society of Dermatology 10, 889-897 (2007).

(2) Timko, A.L., Miller, C.H., Johnson, F.B., Ross, E.V. In Vitro Quantitative Chemical Analysis of Tattoo Pigments. Arch Dermato 137, 143-147 (2001).

(3) Ross, E.V., Yashar, S., Michaud, N., Fitzpatrick, R., Geronemus, R., Tope, W.D., Anderson, R.R. Tattoo Darkening and Nonresponse After Laser Treatment. Arch Dermatol 137, 33-37 (2001).

(4) Kang, I., Lee, M. Quantification Of Para-phenylenediamine And Heavy Metals In Henna Dye. Contact Dermatitis 55, 26-29 (2006).

(5) Vasold, R., Naarmann, N., Ulrich, H., Fischer, D., Konig, B., Landthaler, M., Baumer, W. Tattoo Pigments Are Cleaved by Laser Light-The Chemical Analysis In Vitro Provide Evidence For Hazardous Compounds. Photochem. Photobio. 80, 185-190 (2004).

(6) Varma, S. Swanson, N.A., Lee, K.K. Tattoo Ink Darkening Of A Yellow Tattoo After Q-switched Laser Treatment. Clin. Exp. Dermatol.  27, 461-463 (2002).


Author: Sara Dudgeon