Objective To investigate the longitudinal clinical manifestations of acute radiation dermatitis （ARD） induced by particle therapy in nasopharyngeal carcinoma patients and to analyze associated risk factors. Methods A longitudinal study design was employed， encompassing nasopharyngeal carcinoma patients who underwent particle therapy at the Shanghai Proton and Heavy Ion Center from Mar to Sept 2023. Participants were assessed weekly （1-12 weeks） following the commencement of radiotherapy and at baseline， prior to the start of treatment. Data collection included the patient demographic questionnaire， the Radiation Therapy Oncology Group （RTOG） grading criteria for acute radiation injury， and the radiation-induced skin reaction assessment scale （RISRAS）. Photographic documentation was utilized to capture changes in the irradiated skin area. The enrolled patients with nasopharyngeal carcinoma were grouped according to different particle therapy regimens. Survival data were analyzed by Log-rank and Cox regression methods， while a linear mixed-effects model was applied to repeated measures data. Results A total of 119 patients with nasopharyngeal carcinoma were enrolled. The overall incidence of ARD was 89.1%， which included 39.5% of grade 1， 45.4% of grade 2 and 4.2% of grade 3. With the extension of time， the severity of ARD peaked at week 7 （RISRAS=13.26±4.512）， then began to decrease， ultimately reaching a lower level. Multiple Cox proportional hazards models were constructed， revealing that proton/heavy ion radiotherapy was associated with a lower risk of ARD compared to photon/proton plus heavy ion radiotherapy （HR=0.19，95%CI：0.04-0.92， P=0.039）. Additionally， concurrent cisplatin/nedaplatin chemotherapy was identified as a risk factor for the development of ARD. Least squares （LS） mean differences were calculated at different time points， and the results demonstrated that the RISRAS scores of the photon/proton plus heavy ion group were consistently and significantly higher from week 5 to week 7 compared with the proton plus heavy ion group， and despite a decrease by week 8， statistical differences remained （week 5： LS mean difference 3.35， 95%CI：0.94-5.76，P=0.007； week 6： LS mean difference 5.23， 95%CI：2.20-8.26，P=0.001； week 7： LS mean difference 7.13， 95%CI：3.67-10.59，P<0.001； week 8： LS mean difference 4.04， 95%CI： 0.74-7.34， P=0.017）. Patients undergoing concurrent cisplatin chemotherapy had higher RISRAS scores from week 7 to week 8 of radiotherapy compared with those not receiving chemotherapy ［week 7： adjusted mean difference （Adj.MD） 4.20， 95%CI：1.96-6.57，P=0.006； week 8： Adj.MD 2.79， 95%CI 0.55-5.03，P=0.015］. Similarly， patients on concurrent nedaplatin chemotherapy had higher RISRAS scores from weeks 6 to 7 compared with those not on chemotherapy （week 6： Adj.MD 3.75， 95%CI：1.54-5.96，P=0.001； week 7： Adj.MD 4.41， 95%CI：2.12-6.70，P<0.001）. Skin care measures during treatment and accompanying symptoms such as weight loss were not statistically associated with the development of ARD. Conclusion Proton/heavy ion radiotherapy has a lower risk of ARD， while concurrent cisplatin/nedaplatin chemotherapy is a risk factor for ARD.