The difference between Bio-Oil and Mederma is that Bio-Oil is a facial oil that uses a blend of mineral oil and plant oils like rosemary and lavender while Mederma is a scar gel that uses Cepalin® (onion extract) and humectants like allantoin. Both are popular and affordable scar products with thousands of positive reviews, however, the medical research isn't particularly strong for either one. That said, you can use Bio-Oil for stretch marks, dry skin, and minor scars, while Mederma may help with burns, cuts, scrapes, and even old scars. But if you're looking to get the best results for your scars, consider a silicone gel like ScarAway instead as silicone is the #1 recommended ingredient for scar treatment by medical professionals.
Here's a good analogy:
For high risk scars (e.g. hypertrophic scars and keloids from surgery, accidents, or acne), the gold standard for effective scar management is a silicone gel or silicone sheet.
That's because silicone is safe, supported by decades of clinical studies, and recommended by leading dermatologists in the International Clinical Recommendations on Scar Management.
Finally, PurCellin Oil, the company's "breakthrough ingredient", is actually a synthetic ester called cetearyl ethylhexanoate that's very commonly used to reduce a formula's consistency. (source: Dr. Steve Humphries)
Based on my review of the key ingredients, there's nothing special about Bio-Oil that would support its advertised effectiveness for scars, stretch marks, or uneven skin tone.
In short, Bio-Oil is a mineral oil blended with plant and essential oils plus a viscosity adjuster.
Now, let's discuss the clinical trials provided by the manufacturer:
All studies (except #2) focused on Bio-Oil's effectiveness for reducing scars and stretch marks. However, I found a number of problems with these studies:
Perhaps in response to these types of criticisms, Bio-Oil authorized a second study at the proDERM Institute for Applied Dermatological Research in Hamburg, Germany.
In this study, 80 volunteers with non-hypertrophic scars and stretch marks applied Bio-Oil on treatment scars for 8 weeks (with no treatment on control scars).
Here were the final results after 8 weeks:
Overall, Bio-Oil only produced a small improvement in scar scores (5% and 14%) compared to a control of no treatment (the lowest performance benchmark).
In addition, here's how patients responded to a follow-up questionnaire (% who agreed):
Most patients agreed that Bio-Oil provided a hydrating effect but only 51% believed it improved their scars or stretch marks, while 17% actually said Bio-Oil had no effect at all!
Finally, here's my personal opinion of Bio-Oil based on 3+ months of usage:
My Verdict: All things considered (the key ingredients, clinical studies, and my own experience), I recommend using Bio-Oil for dry skin only because there's insufficient scientific evidence to support its advertised effectiveness for scars and stretch marks.
If you're looking for a scar treatment, keep reading as I'll review Mederma in the next section.
In other words, I recommend using Mederma for less serious wounds, such as mild burns, cuts & scrapes, bruises & accidents, and other minor injuries.
That's because the key ingredient in Mederma Advanced Scar Gel is onion bulb extract (a.k.a. Cepalin in Mederma's marketing materials and allium cepa in the ingredient list).
According to the 2014 International Clinical Recommendations on Scar Management (Part 2), a highly influential research paper authored by the world's leading experts on scar treatment, there's conflicting evidence on the effectiveness of onion extract for scars.
Some studies showed positive evidence, like the original clinical trial by Draelos et al. (2012) that was sponsored by Merz Pharmaceuticals (the parent company of Mederma).
In short, this study found a statistically significant difference in scar appearance between Mederma-treated scars (test group) and non-treated scars (control group) after 4-8 weeks.
However, there's a number of major flaws with this study:
Other studies found that onion extract was no better than similar topical treatments but resulted in more frequent side effects (itchiness, redness) that caused patients to stop using it. (source: International Wound Journal, 2021)
In addition, many studies used multiple active ingredients in their formulations which made it more difficult to isolate the effects of onion extract. (source: Dermatologic Surgery, 2014)
Finally, here's my personal opinion of Mederma Advanced Scar Gel based on 6+ months of using it on my chest keloids:
My Verdict: Taking into account the key ingredients, clinical studies, and my own experience, I recommend Mederma Advanced Scar Gel for low risk scars as the medical evidence is mixed. Mederma may help minimize scars from minor injuries and accelerate the recovery process.
For high risk scars, however, I recommend using a silicone gel or silicone sheet because it's safe (no side effects), clinically proven for scar treatment, and reasonably affordable.