Does Systemic Isotretinoin Treatment Constitute a Predisposition to Allergic Sensitization

13-cis-retinoic acid (13-cRA) is a safe treatment for severe acne, as it has immunomodulatory effects such as enhancing the antigen-presenting activity of epidermal Langerhans cells (LCs) and T-cell activity. The aim of this study was to prospectively show the alteration of sensitization and irritation reactions in acne patients undergoing 13-cRA therapy. This cross-sectional descriptive study consisted of 65 severe to refractory acne patients. The standard thin-layer rapid-use epicutaneous test (T.R.U.E. test) was used to screen sensitization and irritation reactions before and after 3-month 13-cRA treatment. Patch test results after 13-cRA therapy revealed an increase in newly formed sensitization and irritation reactions. Sensitization rate was significantly higher (43.1%) in the second patch test, when compared with the first patch test results (27.7%; P = 0.002). No statistical difference was found in irritation rates. In this study, the sensitization rate was higher after treatment, which could be attributed to the greater antigen penetration due to the disrupted barrier and/or the upregulation of antigen-presenting activity in LC. This would cause a more prominent immune reaction to antigens. Based on these findings, we suggest that 13-cRA may have a sensitization effect, and physicians should be aware of this complication due to 13-cRA treatment. (SKINmed. 2021;19:-0).