Now that a significant percentage of patients are using some form of complementary and alternative medicine — known as CAM — it behooves their physicians to inform themselves about these approaches to better supervise their care.
Scarring is a big deal for many patients for a variety or reasons: Scars may be painful, itchy or unsightly. Your patients will ask you about scarring and what they can do about it; some will want to know if there is anything “natural” they can rub on their scars. In this article, we will discuss common topical agents that are available over-the-counter for scarring and will also discuss the evidence behind these agents.
Vitamin E preparations are probably the most popular among the public for use in improving the cosmetic appearance of scars.1-3 Vitamin E is made up of four pairs of racemic stereoisomers that are derivatives of tocol and tocotrienol and is part of a class of related compounds, the tocopherols, of which alpha-tocopherol is the most important component.1,4,5 The most common preparation of vitamin E is in the form of topical alpha-tocopherol prepared in a cream or oil base.
Early quantitative studies have shown that vitamin E applied topically penetrates deep into the dermis and subcutaneous tissue, which is likely what led to the idea that vitamin E may improve wound healing when applied topically.1
But the effect of vitamin E on wound healing is much more complex than this. When the skin is injured, free oxygen radicals released by neutrophils in the inflammatory phase decrease healing by damaging DNA, cellular membranes, proteins, and lipids, leading ultimately to cell death.2 This damage is theorized to be reduced by antioxidants, of which vitamin E is the main lipid-soluble antioxidant in the skin, thus enhancing wound healing.1,6-9
Although the in vitro antioxidant effects of vitamin E have been well investigated, research on the in vivo effects on skin healing is sparse.1,8,9 Additionally, animal studies have shown that topical vitamin E inhibits fibro-blasts and keratocytes (resulting in decreased scar formation) but have been largely unhelpful because tocopherols, unlike other vitamins, have species- specific mechanisms of action.1,5,10,11
Studies have also shown that topically applied vitamin E provides no more effect than other emollient-type ointments, and hydration appears to be its only beneficial effect.2 Interestingly, topical vitamin E may actually cause more harm than good, possibly worsening a scar’s appearance and causing contact dermatitis, contact urticaria, and erythema multiform-like reactions in a large percentage of patients.1,2,8,9,12-16 A recent report from Widegrow et al has highlighted the skin irritation and reduced tensile strength caused by vitamin E.12 Use of vitamin E later on in the scar’s maturity (4 to 6 weeks and later) may flatten the scar because of its hydrative capabilities, but it may result in a stretched and weakened scar because of its decreased tensile strength effect on the scar; and if used too early, wound separation can occur.12
Bottom Line: Although many patients believe vitamin E speeds wound healing and improves the look of a scar, current evidence from the literature does not support this idea. In fact, studies report adverse effects with use of vitamin E. Because of this, discourage your patients from using topical vitamin E on healing wounds and scars.
Silicones are synthetic polymers based on a dimethyl siloxane monomer and containing a silicon-oxygen backbone, with organic groups attached directly to the silicon atom by silicon-carbon bonds.18 Depending on the length of the chain and the degree of cross-linking, the silicone can be a fluid, gel or rubber.18
Several studies illustrate that treatment of hypertrophic and keloid scars with silicone gel clinically improves the appearance and bulk of the scars, especially in patients with scars from a burn.19,27 The superiority of one form of silicone gel dressing over another, or of a silicone over a nonsilicone gel dressing, however, is controversial. Although both silicone gel sheeting and silicone gel cushions clinically improved hypertrophic and keloid scars, another study indicated no significant difference in efficacy between the two forms of silicone dressing.18
Silicone dressings are believed to decrease scars via wound hydration, increased static charge (i.e., silicone gels contain increased negative static charge), and modulation of growth factors.18,19 A meta-analysis of scar treatment with silicone gel dressing versus gel sheets in the Cochrane Database included 13 trials with a total of 559 subjects and concluded that most studies were of poor quality, making the efficacy of silicone gel sheeting over silicone gel unclear.20
Materials other than silicones (i.e., polyurethane) have shown to be equally effective in the treatment of hypertrophic scars.23,28-30 Both silicone and nonsilicone gel dressings have been effective in reducing scar size, induration, and symptoms over controls, but no significant differences have been noted between results from treatment with silicone and treatment with nonsilicone gel dressings.23
Bottom Line: There is good evidence showing the efficacy and safety of topical silicone for the treatment of hypertrophic and keloid scars. Silicone gel may improve the thickness, color, and texture of scars, especially thick ones. Tell your patients to apply silicone gel to the scar for 8 to 24 hours per day and remind them it may take several months to see improvement. Although early treatment is ideal, silicone gel sheeting may still be beneficial for older scars. Further investigation is needed to demonstrate their effectiveness over nonsilicone gel dressings.
The newest, very popular, and heavily marketed over-the-counter scar treatment consists of onion extract in a topical gel and has been marketed as a product to improve scar appearance and texture (Mederma, Merz Pharmaceuticals).31 The active ingredient, Allium cepa, is derived from a specific type of onion, with the main constituent being quercetin, a bioflavonoid with antiproliferative, anti-inflammatory, and anti-histamine effects in both normal and malignant cells of various types.8,31 Quercetin is also found in apples, red wine, and gingko biloba.8,31
The significance of quercetin’s cellular effects seem to reside in its anti-histamine properties.31 The theory behind this is that a compound that blocks histamine release may normalize or decrease collagen production by fibro-blasts, subsequently resulting in reduced dermal scar volume and relative normalization of the scar maturation process. The cosmetic result is a decrease in scar redness and hypertrophy.31,32 These studies were done in animal models, and there are no reported mechanisms of action describing how onion extract acts to reduce scarring.
Wounds treated with Mederma and then examined histologically did show significantly better improvement of collagen organization.8 However, a prospective, double-blind study of Caucasian males conducted in 2006 demonstrated that the effects of topical onion extract on cosmetic appearance, erythema, and hypertrophy of scars in new surgical scars were equivalent to those of petrolatum emollient.33 These findings contradict the pilot study (conducted in 1999) comparing topical onion extract with petrolatum in which topical onion extract caused no improvement in scar erythema or pruritus, while petrolatum reduced scar erythema.34
Bottom Line: Products containing onion extract (i.e., Mederma) have not been shown to improve scar symptoms in humans and have not shown any benefit over petrolatum emollients. Tell your patients that applying this product to their scars will likely not cause any harm but will not improve them. More research is needed in human tissue about the theorized effects of the active ingredient in the onion extract.
Honey has been used as a dressing for wounds and burns for centuries.
Honey’s effects on wound healing are theorized to be from its antibacterial activity via the small amounts of hydrogen peroxide that is produced in it by the enzyme glucose oxidase in addition to its hydrating properties.35-38
A recent review evaluated the results of 22 clinical trials involving more than 2,000 patients. This randomized and controlled mix of animal and human models — none from studies that were double-blinded) — concluded that honey rapidly clears existing wound infections and protects against further infection, reduces swelling and minimizes scarring, removes infected and dead tissue and speeds healing by stimulating new tissue growth.36
A 1996 study from India showed that burns treated with honey healed sooner than those treated with conventional methods (petrolatum and gauze) and that scarring was reduced; 6.2% of the 450 patients treated ended up with scars compared to 19.7% of the same number of patients who received conventional treatment.37
Bottom Line: More well-designed, double-blind controlled trials in humans are needed, but preliminary studies are promising regarding honey and its wound healing and scar improvement properties. Tell your patients that applying honey to a healing wound or existing scar has not shown to be harmful and may speed healing and improve scar appearance.
Other Possible Candidates
Preliminary and anecdotal evidence supports the use of various herbal preparations to treat scars, but no clinical trials have been performed.
Spathodea campanulata Beauv (Bignoniaceae) A French group reported improved wound healing in the rat burn model with extract from the bark of the African tree, Spathodea campanulata Beauv (Bignoniaceae).39
Centella asiatica. The extract of this plant native to Asia has been shown to improve wound healing in multiple reports.12,40 Most recently, a Korean group reported the clinical effectiveness of treating hypertrophic scars and keloids with titrated extract of Centella asiatica.41
Anogeissus latifolia. The extract of the bark of this deciduous tree native to India has been used for a variety of skin diseases for centuries. The active compounds in the bark are leucocyanin and ellagic acids, which have been shown to have antioxidant and antimicrobial properties.8 There is one report in the literature demonstrating the ability of the bark extract to accelerate wound healing, decrease wound surface area, and increase tensile strength in rat dermal wounds.42
Channa striatus. Enhanced wound contraction with haruan (Channa striatus) fish extract combined with cetrimide cream has been reported using a rat model.43
Citrus limon (lemon). Lemon’s role as an antimicrobial agent has been widely reported.44,45 However, despite numerous anecdotal reports, there is only one case report in the medical literature involving the use of lemon juice on keloids.46
Lime juice, cucumber juice, cocoa butter, and aloe vera. Anecdotal reports abound regarding rubbing these substances on scars, but there are no studies done on any of these to date except for aloe vera. A 1996 report showed enhanced wound contraction in rats treated with aloe vera.47
Bottom Line: Further quality research studies are needed in humans before any of these herbal preparations could be recommended to patients.
What works? The bottom line
To summarize, silicone gel has the most data behind it as an efficacious topical, over-the-counter treatment option for scars, and is an option for patients who want something they can buy themselves. Also, there is probably not any harm, and possibly some benefit, to rubbing honey onto healing wounds and scars. Further quality studies involving human subjects are needed for topical, natural preparations for scars, so in the meantime, encourage your patients to not waste their time or money on other natural products out there that claim to improve the look of their scars.
Dr. Taylor is a dermatology clinical research fellow at Wake Forest University School of Medicine, Winston-Salem, N.C.
Shih R, Waltzman J, Evans GR. Review of over-the-counter topical scar treatment products. Plast Reconstr Surg. 2007; 119(3):1091-1095.
Zurada AB, Kriegel D, Davis IC. Topical treatments for hypertrophic scars. J Am Acad Dermatol. 2006;55(6):1024-1031.