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Tattoo side effects worldwide: a Google Trends-based time series analysis.

INTRODUCTION
It is not known whether tattoo-related complications are becoming more frequent and, if so, how quickly.


METHODS
Data generated through Google Trends (GT) worldwide, from January 1st, 2004 to December 31st, 2018, were analyzed for the search volume indexes (SVIs) of selected symptoms ("swollen tattoo," "raised tattoo," "tattoo bumps," "itchy tattoo," "tattoo fading"), diagnosis ("infected tattoo," "tattoo allergy"), and control terms ("tattoo care," "tattoo healing").


RESULTS
For 2004-2018, the mean SVIs for symptoms were: "itchy tattoo" (41) > "tattoo bumps" (31) > "raised tattoos" (30) > "tattoo fading" (24) > "swollen tattoo" (22). The mean SVIs by 5-year periods showed a regular and constant increase for "itchy tattoo." The search for "infected tattoo" saw a slight but progressive increase, whereas the search for "tattoo allergy" remained stable between 2004 and 2018.


CONCLUSION
Analysis of GT shows an increased search for symptoms such as itching, bumps, and induration on tattoos. However, it cannot be confirmed whether this rise points to a real increase of side effects, or to the popularity of tattoos and generalization of internet use as a tool to obtain information. GT could be of interest for detecting and following trends related to tattoo complications. Use of informal terms rather than medical terms is warranted.