I was speaking to a retired dermatologist who said that a lot of patients came into his office for tattoo removal. He mentioned that many people with tattoos become allergic to the barium, a heavy metal, in the ink and needed to have it removed. I hadn't heard of this so I went to PubMed and Google Scholar to find out more.
A PubMed search yielded only one result about the effects of barium in tattoos (Smitz, 2016). In it is reported a rare case where a 24 year old developed squamous cell carcinoma seven months after receiving a tattoo on the back of her foot. They examined the red dye and, while it primarily consisted of barium sulfate, the dye also contained traces of the elements aluminum (Al), sulfur (S), titanium (Ti), phosphorus (P), magnesium (Mg), and chlorine (Cl). Their conclusion was that, in those rare cases of squamous cell carcinoma, the possible carcinogenic effects of the red tattoo inks are caused by multiple, interacting factors. In other words, it wasn't just caused by the barium in the ink.
Other studies showed that people had reactions to blue, black, red or green inks or inks which used gold. Reactions included lichenoid reactions, contact allergic dermatitis, photoallergic dermatitis, allergic sensitivity to dichromates in green tattoos or allergic sensitivity to carbon black nanoparticles in black tattoos. The allergic reaction to the dichromates in green tattoo ink has been documented as far back as 1960. In Europe, the most common allergic reaction to metals used in tattoos is to nickel (20%), followed distantly by cobalt (7%) and chromium (4%).
The reason it takes awhile for allergic reactions to happen to red ink, it's postulated, is that the allergen is formed inside the skin, either through metabolism, haptenation, or both, over a period of months or years. Allergic reactions to metals develop after sensitization to the metal(s) increase over a period of 10-20 years.
For people who would like to have their tattoos removed, laser treatment is the most common method of removal. Other methods such as dermabrasion, chemical destruction, salabrasion, thermal destruction, and cryotherapy yield inconsistent results, scarring and/or discoloration of the skin, oftentimes pain and ink retention.
It's important to realize that laser removal requires several sessions. Even then, complete removal of all the colors isn't guaranteed. A group of researchers (Kirby, 2009) has even proposed a scale in order to predict how many laser sessions it might take to remove a tattoo in order to help calculate the cost of removal.
Finally, there are the complications resulting from tattoo removal by laser. Khunger, et al, say it best:
Acute complications include pain, blistering, crusting and pinpoint hemorrhage. Among the delayed complications pigmentary changes, hypopigmentation and hyperpigmentation, paradoxical darkening of cosmetic tattoos and allergic reactions can be seen. Another common complication is the presence of residual pigmentation or ghost images. Scarring and textural changes are potential irreversible complications. In addition, tattoo removal can be a prolonged tedious procedure, particularly with professional tattoos, which are difficult to erase as compared to amateur tattoos. Hence the adage, stop and think before you ink holds very much true in the present scenario.
If you get a tattoo, you better hope you don't get allergic to it.
References
Ferraglio, A. (2016). Tattoos from a medical-toxicological point of view. Aesthetic Medicine, 2(4), 123-129. http://www.lamedicinaestetica.it/images/files/files-portale/AE_4_2016.pdf#page=35
Forbat, E., Al-Niaimi, F. (2016). Patterns of Reactions to Red Pigment Tattoo and Treatment Methods. Dermatol Ther (Heidelb) 6, 13–23. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4799043/
Hutton Carlsen, K., Serup, J. (2013). Photosensitivity and photodynamic events in black, red and blue tattoos are common: A ‘Beach Study’. Journal of the European Academy of Dermatology and Venereology, 28(2), 231-237. http://onlinelibrary.wiley.com/doi/10.1111/jdv.12093/full
Kirby, W., Chen, C., Desai, A., Desai, T. (2013). Causes and Recommendations for Unanticipated Ink Retention Following Tattoo Removal Treatment. J Clin Aesthet Dermatol. 6(7): 27–31. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3718753/
Kirby, W., Desai, A., Desai, T., Kartono, F., Geeta, P. (2009). The Kirby-Desai Scale: A Proposed Scale to Assess Tattoo-removal Treatments. J Clin Aesthet Dermatol, 2(3): 32–37. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923953/
Khunger, N., Molpariya, A., Khunger, A. (2015).Complications of Tattoos and Tattoo Removal: Stop and Think Before you ink. J Cutan Aesthet Surg. 8(1): 30–36. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4411590/
Kumar Thakur, B., Verma, S. (2016). Tattoo Practices in North-East India: A Hospital-based Cross-sectional Study. J Cutan Aesthet Surg. 9(3): 172–176. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5064681/
Loewenthal, L. J. A. (1960). Reactions in Green Tattoos: The Significance of the Valence State of Chromium.
Ruby Kaur, R., Kirby, W., Maibach, H. (2009). Cutaneous allergic reactions to tattoo ink. Journal of Cosmetic Dermatology, 8(4), 295-300. http://onlinelibrary.wiley.com/doi/10.1111/j.1473-2165.2009.00469.x/full
Tammaro, A., Tuchinda, P., Persechino, S., Gasparp, A. (2011). Contact Allergic Dermatitis to Gold in a Tattoo: A Case Report. International Journal of Immunopathology and Pharmacology, 24(4), 1111-1114. http://journals.sagepub.com/doi/pdf/10.1177/039463201102400432