Patch test sensitization and permanent tattoos: epidemiological data from two referral centers

SUMMARY

Background. Permanent tattoos introduce pigments and metal contaminants into the dermis, potentially triggering allergic contact dermatitis (ACD). However, comparative analyses between tattooed and non-tattooed individuals remain limited. This study aimed to assess the impact of tattoos on allergic sensitization and patch test (PT) reactivity. Methods. Retrospective observational analysis of 485 adults undergoing PT at two referral centers in Milan (December 2024-June 2025) was included in this study. Patients were classified as tattooed (n = 107) or non-tattooed (n = 378). Patch testing was performed according to the 2024 Italian Baseline Series; reactions were graded following International Contact Dermatitis Research Group guidelines. Logistic regression was performed to identify factors associated with positive reactions, adjusting for MOAHLFA characteristics (male sex, occupational dermatitis, atopic dermatitis, hand/leg/face dermatitis, age > 40 years). Given the retrospective design, the analyses are subject to potential selection bias and unmeasured confounding. Results. Sensitization rates to standard allergens did not differ between the two groups analyzed. However, receiving the first tattoo > 5 years prior 2025 was associated with a 4.4-fold higher risk of nickel sensitization (p = 0.029, OR = 4.407, 95%CI 1.166-16.656). Conclusions. Tattoos do not appear to significantly influence sensitization to standard allergens; however, long-term tattoo exposure is associated with an increased rate of nickel sensitization. These findings may reflect differences in cumulative nickel exposure over time, potentially related to the timing of tattooing and regulatory changes. Consideration of tattoo history and temporal exposure is recommended when assessing ACD risk.

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