Background: Hypertrophic scars and keloids are postsurgery problems. Some studies showed that onion extract and aloe vera might be beneficial for postoperative scars. However, few of the randomized clinical trials were investigated.

Aims: To compare the efficacy of silicone gel containing onion extract and aloe vera (SGOA) to silicone gel sheets (SGS) to prevent postoperative hypertrophic scars and keloids.

Methods: The prospective randomized assessor-blind controlled trial was conducted with 40 patients who had undergone surgery. The patients were divided into two groups: one treated with SGOA, the other with SGS. The patients were evaluated after 1, 2, and 3 months. The objective assessment was to determine the incidences of scarring, erythema, and melanin values using Mexameter, and pliability through Cutometer. The subjective assessment consisted of the patient and observer scar assessment scale (POSAS) and patient satisfaction.

Results: After the 12-week follow-up, there was no statistically significant difference in the scarring incidence rate of both groups. There were no statistical differences in the POSAS score, erythema, and melanin value between both groups. Using objective assessment, pliability in the SGOA group was statistically significantly higher compared to the SGS group. Pain and itchiness significantly decreased in both groups. No adverse effects were reported in either group.

Conclusion: Silicone gel containing onion extract and aloe vera is effective as SGS for postoperative scar prevention.