Scar creams work primarily by trapping moisture in the skin over a healing wound, which sends signals to skin cells to slow down their production of the tough protein fibers that make scars thick and raised. The specific ingredients vary between products, but the core mechanism comes down to hydration, occlusion (creating a barrier that locks water in), and in some cases, reducing inflammation. How well they work depends on the type of scar, when you start using them, and which ingredients are involved.
The Hydration Mechanism
When skin is injured and healing, the outer barrier doesn’t function normally. Water escapes more easily from the damaged area, and the skin dries out. That dehydration triggers cells in the outer layer of skin (keratinocytes) to release chemical signals called cytokines. Those cytokines travel deeper into the skin and tell fibroblasts, the cells responsible for building new tissue, to ramp up collagen production. The result is an overproduction of collagen, which is what creates a raised, firm scar.
Scar creams interrupt this cycle. By forming a protective layer over the scar, they trap water in the outer skin and create a moisture reservoir. With hydration restored, the keratinocytes dial back their signaling, fibroblasts produce collagen at a more normal rate, and the scar tends to flatten and soften over time. This is why consistency matters: the barrier needs to stay in place for hours each day to keep moisture levels stable.
Silicone: The Most Studied Ingredient
Silicone-based products, whether in gel or sheet form, are the most widely recommended topical option for scar management. International clinical guidelines list silicone as a well-established first-line treatment for hypertrophic (raised) scars and a standard tool for scar prevention after surgery. Its primary action is occlusion. Silicone doesn’t penetrate the skin or interact chemically with scar tissue. Instead, it sits on the surface and creates a seal that prevents water loss, normalizing the environment underneath.
This simplicity is actually its strength. Because silicone works through a physical barrier rather than a chemical reaction, it carries very few side effects. A Cochrane review comparing silicone gel sheeting to other options found it may slightly reduce overall scar severity compared to plant-based extracts, though the evidence was graded as low certainty due to small study sizes. In practice, many dermatologists consider it the safest and best-supported option for home use.
Onion Extract and Allantoin
Many over-the-counter scar creams (Mederma being the most recognizable) use onion extract as their active ingredient. Onion extract has demonstrated anti-inflammatory, antimicrobial, and antiproliferative properties in lab studies. It works differently from silicone: rather than simply trapping moisture, it actively reduces levels of histamine and inflammatory signaling molecules like IL-6 in the skin. It can also inhibit the production of growth factors that drive abnormal tissue proliferation, which is relevant for preventing keloids.
Allantoin, often paired with onion extract, adds moisturizing and immune-modulating effects. Together, these ingredients aim to improve collagen organization within the scar, making it smoother and less noticeable. The clinical evidence for onion extract is more mixed than for silicone. Head-to-head trials are small, and while some users see meaningful improvement, the results are less consistent than with silicone-based products.
Why Vitamin E Isn’t a Good Choice
Vitamin E is one of the most popular home remedies for scars, but the research doesn’t support it. Human studies using topical vitamin E have found either no benefit for scar appearance or, in some cases, worse cosmetic outcomes. To make matters more frustrating, vitamin E preparations cause a relatively high rate of skin reactions, including allergic contact dermatitis and redness. These reactions may stem from oxidation byproducts that form in the solution or from the cream base used to deliver the vitamin. If you’re choosing between vitamin E and a silicone gel, the silicone has a far better track record.
When to Start Using Scar Cream
Timing matters. You should not apply scar cream to an open wound. If your incision was closed with dissolvable stitches and adhesive strips, treatment can typically begin about two weeks after the strips come off, as long as the skin is fully closed. If permanent stitches were used, you can start after they’re removed, following your surgeon’s guidance. Applying product too early can trap bacteria under the barrier and increase infection risk.
Starting early in the healing process gives you the best chance of influencing collagen production while it’s still active. Scars continue to remodel for nine to twelve months after the initial wound closes. During that window, collagen fibers reorganize and the scar gradually gains strength, changes color, and flattens. Most people begin to see visible improvement from consistent scar cream use within the first two to three months, but the full benefit plays out over that entire remodeling period.
Which Scars Respond to Topical Treatment
Scar creams work best on newer hypertrophic scars: the raised, red, firm scars that stay within the boundaries of the original wound. These are the scars most responsive to hydration and occlusion because the collagen overproduction driving them can still be modulated. Silicone products reportedly improve size, redness, hardness, and itchiness in these scars.
Keloids, which are scars that grow beyond the original wound edges, are harder to manage with topical products alone. International guidelines recommend injected corticosteroids as the preferred first-line treatment for keloids, with silicone products serving a supporting role. Atrophic scars (indented scars, like some acne scars) don’t involve excess collagen, so a cream designed to slow collagen production won’t fill them in. These typically require procedures like laser resurfacing or microneedling.
Deep burn scars present their own challenge. Superficial burns usually heal without hypertrophic scarring, but deeper burns often require skin grafts or surgical revision. Topical creams can be part of the aftercare but are rarely sufficient on their own for severe burns.
Sun Protection During Healing
UV exposure can darken a healing scar permanently. New scar tissue contains less melanin and is more vulnerable to sun damage than surrounding skin. Applying sunscreen with SPF 30 or higher over healing scars whenever they’ll be exposed to sunlight helps prevent hyperpigmentation. This is especially important for people with darker skin tones, who are more prone to post-inflammatory color changes. Some scar products now include SPF, but a separate sunscreen applied over the scar cream is a reliable approach.
Getting the Most From Scar Cream
The biggest factor in whether scar cream works is consistent, long-term use. Most products are designed to be applied at least twice daily for a minimum of two to three months. Silicone sheets are typically worn for 12 or more hours per day. Skipping days or stopping after a few weeks won’t give the hydration mechanism enough time to influence collagen remodeling.
Pairing topical treatment with gentle pressure can improve results. Applying petroleum jelly or silicone gel under a pressure garment or elastic bandage has been shown to reduce raised scars more effectively than either approach alone. Gentle massage of the scar, once fully healed, can also help break up collagen bundles and improve pliability. None of these steps are dramatic on their own, but together they create conditions that favor a flatter, softer scar over time.