Mederma works by delivering onion extract and allantoin to scar tissue, where plant-based compounds slow down the overactive cell growth that makes scars thick and visible. The gel’s primary strategy is chemical: it targets the biological processes that cause excess collagen buildup in healing skin. Whether it delivers dramatic results is a more complicated question, but understanding the mechanism helps you set realistic expectations.
The Key Ingredients
Mederma Advanced Scar Gel contains two functional components. The active ingredient is allantoin at 0.5%, a compound that hydrates skin, promotes wound healing, and soothes irritation. The ingredient doing the heavier lifting for scar reduction is listed among the inactive ingredients: onion bulb extract (Allium cepa). This extract contains flavonoids, particularly quercetin and kaempferol, which are responsible for Mederma’s effects on scar tissue.
The rest of the formula includes water, a form of vitamin B5 (panthenol), hyaluronic acid for moisture, and standard gel-forming and preservative ingredients. It’s a relatively simple formulation built around two core ideas: calm the scar tissue down and keep it hydrated.
How Onion Extract Affects Scar Tissue
Scars form when your body overreacts during wound healing. Cells called fibroblasts produce collagen and other structural proteins to close a wound, but sometimes they don’t stop when they should. The result is a raised, thick, or discolored scar with too much collagen packed into too small a space.
Quercetin, the primary flavonoid in onion extract, interrupts this process at the cellular level. It slows fibroblast proliferation and reduces collagen production by suppressing two signaling systems that are typically overactive in problem scars. These pathways normally tell fibroblasts to keep multiplying and keep producing structural proteins. Quercetin dials those signals down. Lab studies on keloid fibroblasts (the cells responsible for the most aggressive type of scarring) showed that quercetin-treated cells produced virtually no excess structural fiber, while untreated cells deposited dense layers of it.
Quercetin also provides a mild anti-inflammatory effect. Research suggests the flavonoids in onion extract can inhibit histamine release from immune cells, which reduces local inflammation. Less inflammation means less stimulation for fibroblasts, creating a calmer healing environment where scar tissue is less likely to overgrow.
What Allantoin Does
Allantoin’s role is more supportive than transformative. It hydrates the skin over the scar, softens the tissue, and helps reduce the itching and tightness that often accompany healing wounds. Well-hydrated scar tissue tends to be softer and more pliable, which can improve both how a scar feels and how it looks over time. Allantoin also has mild keratolytic properties, meaning it helps loosen the outer layer of dead skin cells, which can improve the texture of rough or bumpy scars.
What the Evidence Actually Shows
The cellular science behind quercetin is solid in lab settings. Translating that to visible results on your skin is where things get less clear-cut.
A study using an animal model of hypertrophic (raised) scars found that Mederma did not significantly reduce scar height, scar redness, or inflammation compared to untreated scars. It did, however, significantly improve the organization of collagen within the scar. Disorganized collagen is what gives scars their different texture and appearance compared to normal skin, so better-organized collagen could translate to a scar that looks and feels more like the surrounding skin over time, even if it doesn’t shrink dramatically.
A small human study with 44 participants found that applying Mederma three times daily for eight weeks improved scar appearance, softness, and texture. That’s a modest but real benefit, and the massage involved in application likely contributed to the improvement as well, since regular massage alone can help break down scar tissue.
When compared directly to silicone-based scar treatments (sheets or gels), silicone products have generally performed better. One study on burn scars found both silicone gel and silicone sheets more effective than onion extract for treating raised scars. Silicone works through a different mechanism entirely: it creates a physical barrier that locks in moisture and may modulate the growth factors involved in scarring through hydration and pressure.
Which Scars It Works Best For
Mederma is designed for scars that are already closed, not open wounds. The manufacturer recommends it for surgical scars, scars from burns, acne scars, and scars from cuts or other injuries. It comes in formulations for both new and old scars, though newer scars are generally more responsive to any topical treatment because the tissue is still actively remodeling.
For flat or mildly raised scars with discoloration or rough texture, Mederma’s combination of anti-inflammatory effects and improved collagen organization is most likely to produce noticeable results. For significantly raised hypertrophic scars or keloids, the evidence suggests you may see modest textural improvement but not meaningful flattening. Keloids in particular are notoriously difficult to treat with any over-the-counter product.
How to Use It
The recommended application is three times a day. For new scars (once the wound has fully closed), the manufacturer suggests using it consistently for at least eight weeks. For older scars, the timeline extends to three to six months. Consistency matters more than the amount you apply. A thin layer massaged gently into the scar is sufficient.
Mederma PM, the overnight version, is formulated with a proprietary blend called Tripeptol and is designed to work with your skin’s natural repair cycle during sleep. It’s applied once at night instead of three times during the day, which some people find more practical to maintain.
Side Effects
Mederma is generally well tolerated. The most common issues are mild burning, stinging, redness, or irritation at the application site. Allergic reactions are rare but possible, with symptoms like hives, swelling of the face or throat, or difficulty breathing requiring immediate medical attention. If you notice significant irritation, stop using the product. Testing a small amount on nearby healthy skin before applying it to a scar can help you gauge your sensitivity.
Mederma vs. Silicone Products
If you’re choosing between Mederma and silicone-based scar treatments, the comparison comes down to mechanism and evidence. Silicone products create a physical occlusive layer that traps moisture against the scar, keeping it hydrated around the clock. This constant hydration is thought to regulate the growth factors that drive excess collagen production. Silicone sheets and gels have a larger body of clinical evidence supporting their use, and dermatologists often recommend them as a first-line over-the-counter option for raised scars.
Mederma takes a chemical approach, relying on quercetin to actively suppress fibroblast activity rather than simply hydrating the tissue. Both strategies aim at the same outcome (less excess collagen, softer and flatter scars), but head-to-head comparisons have favored silicone. That said, Mederma is easier to apply under clothing and makeup, dries clear, and some people prefer the convenience of a gel over wearing adhesive sheets. For mild scarring or as a complement to other treatments, it remains a reasonable option.