Data collection.

To gain insights into bodily modifications, an exhaustive review of scientific literature on tattoos and their changing conceptualizations was conducted. Other authors have used this type of review to create narrative constructions of the emergence of tattooing and its evolution and, in those cases where the medical aspect predominates, to analyze skin care techniques when tattooing or when dermatological complications occur. A search and selection of articles was performed based on ^{Moher et al.'s (2009)} model (Figure 1).

Source: Based on^{Moher et al. (2009)}

Figure 1 Flowchart of the systematic literature review selection process 

For the identification of scientific articles addressing body issues and their relationship to tattooing, a search for peer-reviewed papers was designed. This search included different methodologies and research disciplines. The identification process involved the selection of a variety of terms that were included in the search equation. The search was conducted in Scopus between 2017 and 2021, yielding a total of 305 documents.

Regarding the selection, in this step, only research articles were considered. Therefore, documents such as proceedings, editorial materials, reviews, book chapters, and other editorial materials were excluded (n=223).

Eligibility was done through two selections. In the first selection, documents that did not specifically talk about tattoos were eliminated, i.e., articles whose main topic was piercings and other types of body modifications (n= 203). In the second selection, the articles were thoroughly read and classified into nine categories: 1. Anthropologic, 2. Gender, 3. Work environment, 4. Medical care, 5. Body modifications, 6. Legal, 7. Forensic Science, 8. Medical conditions, 9. Technical. Of these nine categories, four were discarded (legal, forensic science, medical conditions, and technical) because they were not relevant to the investigation. Finally, in the inclusion section, 152 articles related to the remaining five categories were selected.

Data analysis.

Variables associated with: 1) general characteristics of the articles, and 2) specific variables related to body-tattooing, were coded using the content analysis technique, which allows the identification of main themes, concepts, or variables through a rigorous examination of the text (Riffe et al., 2005). A total of nine categories of analysis were systematically coded in each of the 152 articles (Appendix 1).

Results analysis.

First, a descriptive analysis of the variables of temporal evolution (concentration and dispersion per country) was conducted. This analysis considered the place of publication of the article as opposed to the author's origin (The graph was created using Visme software). Concentration and dispersion by journal were also analyzed. For this purpose, a list was made of the places where the journals containing the articles used for this research were published. This list was then used to search for the publisher. Finally, a keyword co-occurrence analysis by category was performed using VOS viewer software. Subsequently, the articles were systematically classified using analysis sheets. These sheets served to categorize the articles according to the relationships they addressed between body and tattoo.

Time evolution

Within the analyzed articles, 152 documents were found in the period of 2017-2021. Figure 2 shows that publications were constant during these five years.

Figure 1. Time evolution - No. of articles per year

The growing interest in the study of tattooing, as demonstrated by the review of articles, is derived from the boom in the practice of tattooing not only as a merely ancestral, symbolic, and/or cultural exercise but also because of the commercial and capital interest that this practice generates. More and more people are taking up tattooing, establishing the practice as an increasingly sought-after profession. Therefore, tattooing has become an object of discussion that has crossed borders and stereotypes socially assigned to people who modify their bodies, reaching not only artistic communities but also scientific ones.

Concentration and dispersion per country. In terms of concentration and dispersion per country, publications were found in 27 countries. The countries with the highest concentration, that is, with the highest number of articles published on tattooing and its relationship to the body, are in Europe. The United Kingdom was the country with the highest number of articles, with a total of 48 (36.1 %), followed by Germany with 10 articles (7.5 %). The United States also presented a high concentration of publications, with a total of 35 articles (26.3%). Regarding Spanish-speaking countries, only 4% of the articles analyzed were published there.

Source: Own elaboration

Figure 2 Concentration per country 

The dispersion of production per country for this research was high since we found that 19 countries had 2 or fewer publications. It is important to note that the analysis of concentration per country, in this case, was based on the place where the article was published and not on the place of origin of the authors.

Concentration and dispersion per journal. The data collected in this research allowed us to identify the concentration and dispersion of the journals in which the analyzed articles were published. The analysis was limited to those journals that had published at least two articles. The reason behind this is that the journals with only one publication do not provide any compelling evidence of a high concentration. From the total of 152 articles, only 127 journals were identified. Thus, suggesting a diverse range of publications rather than a high concentration in a single number of journals.

According to Appendix 2, the journal "Deviant Behavior" of the University of Louisiana published the highest number of articles analyzed, with 4 articles (2.6%). They are followed by the European Journal of Applied Physiology, Journal of Archaeological Science, and Asia Pacific Journal of Anthropology, each with 3 articles (2.0%). In addition, 11 journals were identified that published 2 articles each (1.3%). The results also showed a high dispersion of 88%.

Keyword co-occurrence network. From the analysis of the keywords contained in the articles, we can establish a network of co-occurrences for each of the analyzed categories in Figure 3, created from the words that appear a minimum of two times in the corpus documents. The keyword tattoo is presented as the prominent center of the network. However, each of the networks show particularities according to the category. For example, the network related to the body modification category is associated with words such as body, piercing, and autopsy, whereas for the network of the anthropological category, words such as identity, motivation, and family are the ones that stand out.

Source: Own elaboration

Figure 3 Co-occurrence of keywords 

Data Analysis

The following is the content analysis derived from the categories mentioned in the documentary search and tracking in the study of tattooing.

Gender

Tattooing is also related to the category of gender, which alludes to or relates to the belief or stereotype that tattoos can be assigned to men, or to women, in order to fulfill a function and/or role according to their sex. Tattoo culture generates distinctive conditions between the two gender roles. Historically, tattoos were predominantly associated with males (^{Witkos & Hartman-Petrycka, 2020}). However, the increase of women sporting tattoos can now be seen as a dismantling of traditional gender norms, particularly when viewed from a stereotypical point of view. This category revealed two subcategories related to gender, demonstrating that tattoos not only modify social perceptions but also assign specific attributes to opposite sexes.

On one hand, there is the subcategory we call "Tattoo as gender resistance" which provides conceptual notions about how both sexes grant a distinctive function to tattooing. ^{Choudhury and Bhattacharyya (2020)}, along with ^{Rahbari et al. (2019)}, examine how women use tattoos as a form of resistance against the suppression of their bodies. A prominent example is the political and sociocultural situation in Iran, where women have no control over their bodies due to the biopolitical state conditions. ^{Maxwell et al. (2020)} conducted a similar study by exploring how tattooing can be an alternative therapeutic medium for women who have experienced sexual violence trauma. In this context, women use tattoos as a way of "reclaiming and asserting control over their bodies." The tattoo defies the "sanctity" that was politically imposed by the state and becomes a symbol of their fight and dignity. It can also be a mean to achieve body perfection in cases of body non-acceptance and disorders related to low self-esteem (^{Geller et al., 2020}; ^{Kertzman et al., 2019}; ^{Merinov & Vasilyeva, 2020}). In addition, tattooing is seen as a symbol of femininity and an expression of personal purpose (^{Dann & Callaghan, 2019})

In contrast to women, tattooed men are perceived as stronger, dominant, masculine, and attractive, according to studies by ^{Galbarczyk et al. (2020)}, ^{Galbarczyk and Ziomkiewicz (2017)}, and ^{Molloy and Wagstaff, (2021)}. However, they are also associated with violent and 'deviant' behaviors. Miller-Idriss (2017) discusses how tattooing contributes to the construction of masculinity in young men, in terms of value formation and experiences of risk. Conversely, the sexualization of tattooing in women has led to research on the bias and marginalization faced by tattooed women across different settings. ^{Lee (2017)} and ^{Tews and Stafford (2019)} explore the sexual attention that visible tattoos generate in women, especially in work contexts. Similarly, the study made by ^{Skoda et al. (2020)} shows how tattooed women receive more sexual attention and are perceived as more "accessible" than non-tattooed women, according to gender stereotypes. Visibly tattooed women can be perceived in two ways: first, as stronger and more confident women, or second, as sexually open and promiscuous, among other negative labels (^{Orr, 2017}).

This final category addresses sociocultural perceptions of tattooing from a gender perspective. Tattooing is presented as a multifocal discourse that can alter the image and notion of individuals based on beliefs and stereotypes. It was found that, in both sexes, tattoos can be perceived as signs of health, attractiveness, and self-confidence, and as symbols of strength and identity. However, they are also associated with violence, promiscuity, low self-esteem, and harmful behaviors.

Medical Care

Articles that respond to medical applications and implications of the practice of tattooing both in living bodies and postmortem have been grouped in this research category. Throughout the analysis of the medical care category, three subcategories were found: psychoimmunological, socioimmunological, and biological.

Regarding the subcategory of socioimmunological, authors such as ^{Birngruber et al. (2020)} and ^{Levy (2020)} recognize that tattoos have positioned themselves as important tools to be used in legal processes. Tattooing is presented as a way for subjects to express their desire not to be resuscitated in case of an emergency. However, there is an ethical discussion about how to proceed when encountering a tattoo that expresses the desire not to be resuscitated, and the question is: How much validity does a symbol engraved in the skin have? These types of non-resuscitation orders continue to be a medical and legal problem since there is a shortage of resources on the subject. However, tattoos can serve as a solution by providing visible information to emergency service professionals who need to make a quick decision about the patient's resuscitation. In this context, tattoos can provide a clear, immediate visual cue, which is crucial given the limited amount of time available during these situations (^{Levy, 2020}).

^{Birngruber et al. (2020)} conducted research in Jalisco, Mexico, to determine the potential role of tattoos in identifying the bodies of unidentified deceased persons. Postmortem data of 2045 bodies from the Jalisco Institute of Forensic Sciences in Guadalajara was evaluated. His study showed that tattoos have a functionality beyond artistic expression or aesthetic taste (^{Ondruschka et al., 2017}), even in postmortem tasks such as identifying bodies.

In the psychoimmunological category, authors such as ^{Komiya and Iwahira (2017)}, ^{Osborn and Cohen (2018)}, and ^{Reid-de Jong and Bruce (2020)} identify the art of tattooing as a tool that favors self-expression, healing, and transformation of people who have gone through diseases that have left phenotypic imprints on their bodies, such as a mastectomy, ocular melanoma, or vitiligo.

Tattoos have played a crucial role in the treatment of breast cancer, being used in both cosmetic reconstruction and radiation treatments. Considered a heteronormative body ideal in society, the absence of mammary glands can have significant emotional consequences for women who have had to undergo mastectomy. These women may feel less feminine, less attractive, and experience decreased sexuality (^{Komiya & Iwahira, 2017}). According to ^{Reid-de Jong & Bruce (2020)}: "Post-mastectomy tattooed bodies enrich the discourse on what constitutes beauty, femininity, and sexuality while offering these women the agency to reclaim their bodies and refine their self-concepts" (p. 695). In breast cancer, tattoos have been used in patients undergoing accelerated partial breast irradiation, in order to aid in alignment and verification of daily settings (^{Jimenez et al., 2019}; ^{Osborn & Cohen, 2018}).

Aesthetic tattoos have been used in the treatment of patients with vitiligo to help them feel better about their bodies and meet beauty standards (^{Ju et al., 2020}; ^{Kluger, 2017}). In addition, corneal tattooing with Rotring drawing ink has been shown to be effective in the cosmetic improvement of disfigured blind eyes, achieving favorable results and high patient satisfaction. This technique is an alternative to more sophisticated cosmetic reconstructive surgeries (^{Rodriguez-Avila et al., 2020}; ^{Santos da Cruz et al., 2017}) and is considered an affordable surgical procedure to improve cosmetic appearance in eyes with disfiguring corneal opacities (^{Alsmman et al., 2018}).

Regarding the biological subcategory, authors such as ^{Yetisen et al. (2019)} identified other uses of tattooing on the body as biosensors. Tattooing is a ubiquitous body modification that involves the injection of ink or coloring pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed to measure pH, glucose, and albumin concentrations. The sensors were multiplexed on a skin tissue sample, and quantitative readings were obtained using a smartphone camera.

Work environment

The analysis of the work environment category showed how tattoo body art can influence the labor market, affecting aspects such as selection during a job interview, salary perception, bosses' perceptions of their employees, and the general work environment. Although it is recognized that visible body modification is an expression of sociocultural trends, as well as an individual's personal experiences, values, expectations, and knowledge, attitudes toward such body modifications can influence hiring practices (^{Uzunogullari & Brown, 2021}). In the analysis of the influence of tattoo body art, two main trends were identified: tattooing as a stereotype that carries stigmatization and tattooing as a common practice in modern society.

Regarding tattooing as a stigmatizing stereotype, authors such as ^{Hauke-Forman et al (2021)}, ^{Henle et al (2021)}, ^{Tews & Stafford (2019)}, and ^{Thielgen et al. (2020)} acknowledge that tattooing is not an approved practice within traditional etiquette codes. For, tattooed people, as a loosely constituted social group, are apparently labeled as a disadvantaged community of individuals commonly associated with lower-class countercultural offenders (^{Brown et al., 2010}). Additionally, tattooed individuals are considered to be more likely to engage in risky behaviors compared to their non-tattooed counterparts (^{Mortensen et al., 2019}).

Preconceived religious and sociocultural ideas about people with visible tattoos create negative implications for hiring in the workplace, which could prevent organizations from recruiting and retaining talented employees. This implies that talented employees may experience bias in job interviews, which prevents them from obtaining employment (^{Adisa et al., 2021}). According to ^{Tews and Stafford (2019)}, employees with a higher number of visible tattoos tend to receive less favorable treatment, which is reflected in interpersonal relationships and perceived discrimination. Furthermore, these tattooed employees are commonly given reduced pay and judged as less competent in comparison to candidates who do not have visible tattoos (^{Henle et al., 2021}). However, this job and wage discrimination is mainly affected by two factors: the type of profession and the age of the interviewers. Regarding the type of profession, discrimination is more evident in sectors such as health, beauty, retail, and customer service (^{French et al., 2019}).

A study by ^{Hauke-Forman et al (2021)} found that police officers with tattoos and piercings are perceived as less trustworthy and competent. On the other hand, the age of the interviewers also plays an important role. According to a study by ^{Tews et al (2020)}, interviewers from the millennial generation tend to view candidates with light tattoos more positively than older interviewers. Although there are numerous studies that recognize tattooing as a factor of discrimination and unequal treatment in the workplace, more research is still needed to probe further into the subject and include new categories of analysis (^{Thielgen et al., 2020}).

In the work environment category, a trend has been identified that considers tattooing as a practice of the contemporary individual. Authors such as ^{French et al (2019)}, ^{Mironski and Rao (2019)}, ^{Thompson (2020)}, and ^{Timming (2017)} argue that, at present, clothing and tattoos do not define an individual's job competencies. Hence, there has been a notable change in societal views towards this form of body art, gradually altering stereotypes to acceptance (^{Mironski & Rao, 2019}).

Tattooing is positioning itself as a common practice, as people's appearance is becoming less and less important when assessing employee competence, professionalism, caring, approachability, trustworthiness, or reliability (^{Cohen et al., 2018}). This has allowed the body art of tattooing to be used strategically to positively convey the brand of organizations, especially those targeting a younger, edgier audience (^{Timming, 2017}). In addition, it is consolidating new ways of perceiving individuals. For example, Generation X and Millennial teachers with subcultural affiliations and alternative appearances, including visible tattoos, are changing the image of the modern teacher (^{Thompson, 2020}). However, this freedom of dress and body art generally applies to white heterosexual men, while those with increasingly marginalized identities still feel pressured to follow the standard of a more conservative wardrobe (^{Thompson, 2020}).

There are two main trends in this category. The first is a traditional hegemonic trend, based on religious conceptions and socially conservative dress codes. This trend reflects the problems of stigmatization and job discrimination, where people with visible tattoos are considered less competent and reliable, receive lower wages, and are often rejected because of their physical appearance. The second trend is the result of the normalization and acceptance of tattooing as a contemporary artistic practice. This trend is directly related to the generational change in the workplace, as new workers belong to Generation X and Millennials. These generations' view of the body is different from that of older people, which has led to greater acceptance of tattoos in the workplace.

Body modifications

In the analysis of tattoos as a practice of the contemporary subject, tattooing was related to the concept of body modifications, which are understood as invasive interventions on the human body, especially interventions on the human skin that result in (semi-) permanent changes (^{Liebermann, 2021}). Currently, tattoos are understood as fashion adornments, body art, and a mechanism to express pain that integrates a social and cultural reality (^{Aldaz et al., 2021}) that possesses a preference over less dangerous options (^{Lynn et al., 2019}). Therefore, two subcategories were outlined: tattooing as a fashion artifact and as a canvas for expression.

Tattoos have positioned themselves as a fashionable artifact, since people do not always get them with a specific meaning, but rather as a response to an impulse or to enhance their concept of beauty (^{Aldaz et al., 2021}; ^{Henley & Porath, 2021}). For example, tattoos have become a recurring YouTube narrative with a large number of viewers (^{Frankel et al., 2021}). According to studies by ^{Tomaz and Neves (2019)} in schools, tattoo fashion is spreading rapidly as a trend among female minors.

In the subcategory of tattooing as a canvas of expression, the body is perceived not as a biological construct but as an artistic and expressive canvas. On this canvas, narratives detailing experiences, emotions, intimate relationships, challenges, and significant connections are engraved permanently into the skin. Consequently, the tattoo is not a part of the subject's body, but a synthesis of it (^{Keagy, 2020}). Thus, tattoos serve as an expression of personalities and are specifically prevalent among individuals with a need to communicate their individuality (^{Kalanj-Mizzi et al., 2019}) or a sense of group affiliation, as observed in communities such as heroin addicts who often incorporate religious or Christian symbols into their tattoos (^{Katsos et al., 2018}).