To evaluate an Aloe vera lotion for prevention of radiation-induced dermatitis, all patients with a prescription of radiotherapy to a minimum dose of 40 Gy were eligible provided that their treatment area could be divided into two symmetrical halves. Patients were given a lotion of Aloe vera to use on one half of the irradiated area, with no medication to be used on the other half. The grade of dermatitis in each half was recorded weekly until 4 weeks after the end of radiotherapy. The trial enrolled 60 patients (mean age: 52 years; 67% women). Most patients had breast cancer (38%), followed by pelvic (32%), head-and-neck (22%), and other cancers (8%). Field size was 80–320 cm2 (mean: 177 cm2), and the dose of radiotherapy was 40–70 Gy (mean: 54 Gy). Concurrent chemotherapy was administered in 20 patients. From week 4 to week 6 of radiotherapy and then at weeks 2 and 4 after radiotherapy, the mean grade of dermatitis with and without Aloe vera was 0.81 and 1.10 (p < 0.001), 0.96 and 1.28 (p < 0.001), 1.00 and 1.57 (p = 0.006), 0.59 and 0.79 (p = 0.003), and 0.05 and 0.21 (p = 0.002) respectively. Age and radiation field size had a significant effect on the grade of dermatitis. Based on these results, we conclude that the prophylactic use of Aloe vera reduces the intensity of radiationinduced dermatitis.