OBJECTIVE: To investigate the association between allergic diseases and the tendency to self-harm in adolescents, considering the role of sedentary behavior. METHODS: This was a population-based cross-sectional study, carried out in 2022, with 727 adolescents aged 12 to 19 years, from a capital in the Northeast of Brazil. The authors evaluated the association between each allergic disease (asthma, rhinitis and eczema) and self-harm, sedentary behavior and other variables. The authors performed an adjusted analysis of the associations between each allergy disease and the tendency to self-harm and then adjusted to the presence of family members and sedentary behavior. RESULTS: The prevalence of asthma, rhinitis and eczema were 18.76%, 36.21% and 12.86%, respectively. Sedentary behavior and tendency to self-harm were more frequently reported in asthmatics (PR 2.16
95% CI: 1.55 - 3.00 and PR 1.98
95% CI: 1.47 - 2.68, for sedentary behavior and self-harm respectively), rhinitis (PR 1.53
95% CI: 1.25 - 1.88 and PR 1.33
95% CI: 1.09 - 1.62, respectively) and eczema (PR 2.35
95% CI: 1.54 - 3.58 and PR 1.55
95% CI: 1.05 - 2.28, respectively). There was a reduction in the strength of this association in the three conditions, which included a loss of association. CONCLUSION: High rates of sedentary behavior and self-harm in those with asthma, rhinitis and eczema. Physical activity attenuated the risk for self-harm. It warns about the urgency in detecting these factors, whether in the diagnosis or in the implementation of therapy, seeking to reduce their harmful consequences in the short and long term.