Tested on animals:Yes
Keeping wounded skin or a fresh scar protected from sunlight is critical to healing and/or how the scar will change in appearance over time. This sunscreen is one way to do that, and it provides avobenzone for UVA (think anti-aging) protection.
However, believing that it works to make scars look better due to its onion extract may not lead to satisfaction because the research on said onion extract is mixed.
On one hand, a comparative study examining the effects of Mederma’s onion extract with plain Vaseline revealed no difference in scar appearance at the outcome, and other studies have disproven Mederma’s claims about onion extract as well (Sources: Dermatologic Surgery, February 2006, pages 193–197; and Archives of Dermatology, December 1998, pages 1512–1514).
On the other hand, there are studies that show Mederma's onion extract may reduce inflammation and impact collagen remodeling which could reduce the appearance of a scar (Sources: The Journal of Clinical and Aesthetic Dermatology, June 2012, pages 18-23; and Plastic and Reconstructive Surgery, July 2002, pages 177-183). Due to mixed results from the research, we've softened our recommendation on Mederma: Although it's not a slam-dunk, it may prove helpful for some people, but you may have even better results from applying a scar-reducing serum loaded with beneficial skin-healing ingredients, so some experimentation may be needed.
This product deserves a good rating for its merit as an effective sunscreen for normal to dry skin and potential efficacy at improving the appearance of scars.