Volume 36, Issue 8, Page 25 (August 2005)
LESLIE S. BAUMANN, M.D.
DR. BAUMANN is director of cosmetic dermatology at the University of Miami. To respond to this column, or to suggest topics for future columns, write to Dr. Baumann at our editorial offices via e-mail at
Onions—along with other popular edible botanicals, such as garlic, chives, leeks, scallions, and shallots—belong to the lily (Allium cepa) family. Numerous varieties of onions are cultivated worldwide. This aromatic bulb has also been used by traditional Chinese medicine and ayurveda for thousands of years.
Onion extract is a common ingredient in skin care products. But inclusion in topical products does not necessarily translate into efficacy. The extract's status as an included ingredient might be considered cosmetic, so to speak, and it is somewhat more controversial than other botanicals. It is used in cosmeceuticals and in medications in the clinical setting.
The antimicrobial effects of onion have been well accepted for many years (Int. J. Dermatol. 1980;19:285–7), but a fair number of physicians doubt its efficacy in skin care products. Those authors cite the dearth of proven efficacy for one of the more popular onion extract creams, Mederma, for instance (Plast. Reconstr. Surg. 2002;110:177–83, discussion 184–6; Arch. Dermatol. 1998;134:1512–4). Nevertheless, such products are used with increasing frequency for treating hypertrophic scars and keloids.
Although longitudinal data for specific products may not be available, onion extract has been studied for at least the past 25 years.
In a double-blind study of six atopic and six nonatopic adult volunteers, alcohol/onion extract (5% ethanol) was injected simultaneously with 20 IU and 200 IU of rabbit antihuman IgE intradermally. Resultant flares were measured 10 minutes later and compared with control sites injected with 20 IU and 200 IU of anti-IgE in 5% ethanol. All sites were then epidermally treated with 45% alcohol/onion extract and 45% ethanol under occlusion, with wheal sizes showing a marked reduction in the onion-treated skin; late-phase edema formation was also significantly diminished. The researchers concluded that onions have pharmacologically active ingredients that exhibit anti-inflammatory and/or antiallergic properties (Allergy 1984;39:43–9).
Although the sample size used in this study was too small to draw any far-reaching conclusions, subsequent research has provided more substantial data. Indeed, antimicrobial, antithrombotic, antitumor, hypolipidemic, and hypoglycemic activities are now being attributed to various phytochemicals in the Allium genus (Cancer Lett. 2000;160:29–35).
In a study conducted a decade ago, investigators assessed the inhibitory effect of onion oil against the growth of four gram-positive and four gram-negative bacteria as well as nine species of dermatophytic fungi. Onion oil was highly active against the gram-positive bacteria and against one of the gram-negative isolates, Klebsiella pneumoniae. Significant inhibitory effects were also seen against the dermatophytes, with complete inhibition noted against Microsporum canis, M. gypseum, Trichophyton simii, Chrysosporium queenslandicum, and Trichophyton mentagrophytes.
Increases in onion oil concentration also inhibited the growth of four other dermatophytic fungi species (Microbiol. Res. 1995;150:167–72).
The antifungal activity of onion extract has been buttressed by more recent research. Investigators found that the growth of the dermatophytes Trichophyton rubrum and T. mentagrophytes was strongly inhibited by aqueous onion extract in a dose-dependent manner, with T. mentagrophytes more affected at all tested concentrations (Fitoterapia 2004;75:645–55). In addition, significant antifungal activity was exhibited by onion extract in a study in Iran (Iran. Biomed. J. 2003;7:113–8).
Onion's chemopreventive activity has been associated with diallyl sulfide, a compound also found in garlic (Skin Pharmacol. Appl. Skin Physiol. 2001;14:373–85). Skin cancer has been a focus of several studies using this compound (Cancer Lett. 1988;40:193–7). Investigators have shown that the topical application of diallyl sulfide inhibited benzoyl peroxide-mediated tumor promotion in SENCAR mouse skin tumors initiated by 7,12-dimethylbenz[a]anthracene (DMBA) (Nutr. Cancer 1990;14:183–93). Similar inhibitory results have been seen in SENCAR mice with DMBA-induced and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted skin cancer after topical application of diallyl sulfide and the related diallyl disulfide (Biomed. Environ. Sci. 1998;11:258–63; Pharm. Res. 1992;9:1668–70; J. Invest. Dermatol. 1990;94:162–5).
Interestingly, quercetin (SKIN & ALLERGY NEWS, January 2005, p. 18), a bioflavonoid known to exhibit antihistamine release effects and antiproliferative activity on normal and malignant cells, is a derivative of Allium cepa, the active ingredient in Mederma. The pharmacologic properties of quercetin may confer benefits in the treatment of hypertrophic scars, which are discussed below (Plast. Reconstr. Surg. 2002;110:177–83; discussion 184–6).
In a study of nicotine-induced lipid peroxidation, investigators evaluated the antioxidant effect of oils isolated from onion and garlic on rat liver, lungs, heart, and kidney over a 3-week period. Resistance to lipid peroxidation increased in the nicotine-treated rats as a result of garlic oil and onion oil supplementation, which was also associated with elevated glutathione concentrations and increased antioxidant enzyme activity. The researchers concluded that garlic and onion oils effectively exhibit antioxidant activity in tissue characterized by nicotine-induced oxidative damage (Vet. Hum. Toxicol. 1999;41:316–9).
The breadth and depth of research and traditional usage vary widely among the numerous cosmeceutical ingredients that have been discussed in this column, but only a few of the botanicals are included in products used regularly in the clinical setting. Two such products, Contractubex gel and Mederma, contain onion extract.
In a 6-month study, researchers evaluated the ability of scar-specific Contractubex gel—which contains 10% onion extract, as well as sodium heparin and 1% allantoin, another botanical product (SKIN & ALLERGY NEWS, June 2003, p. 10.)—to contribute to scar development in children who underwent thoracic surgery.
Thirty-eight patients treated with Contractubex were compared with 27 untreated patients, with treated scars receiving a better global evaluation than did the untreated scars. The increase in scar size was significantly smaller in treated patients than in untreated patients, and treated scars exhibited quicker lightening. In addition, physiologic scars developed into hypertrophic or keloidal scars more frequently in the untreated group. Contractubex was well tolerated, and its effects persisted through the 6-month follow-up visit (Drugs Exp. Clin. Res. 1995;21:199–206).
In an earlier study of Contractubex gel, 45 young patients who had undergone thoracic surgery were randomized to receive topically applied Contractubex or no treatment. Treatment was initiated roughly a month after surgery and continued for 1 year; scar attributes—including appearance, type, size, and color—were assessed monthly in all patients. Although no differences were observed in scar length or height between the groups, the increase in scar width was reduced in the Contractubex group but not the untreated one. Normal skin-toned scars and those considered physiologic were more numerous in the treated group, whereas hypertrophic or keloidal scars were more common in the untreated group. Contractubex was deemed to be well tolerated and effective for treating postoperative thoracic scars (Int. J. Clin. Pharmacol. Res. 1994;14:193–202).
Recently, the effects of Mederma on 32 hypertrophic scars in the rabbit hypertrophic scar model were evaluated 28 days after initial wounding. All scars were photographed, then half were treated with Mederma three times a day for 4 weeks, and the other half, serving as controls, were left untreated. Scars were photographed again after treatment. No significant reduction in scar erythema was seen in the treated lesions, nor were any significant differences detected in dermal vascularity or inflammation.
Histologic analysis showed no significant reduction in scar hypertrophy or elevation, but dermal collagen organization improved significantly in scars treated with Mederma. Though the results were decidedly mixed, investigators concluded that the improvement in collagen organization indicates that Mederma might influence the pathophysiology of hypertrophic scar formation (Plast. Reconstr. Surg. 2002;110:177–83; discussion 184–6).
In another study of Mederma, investigators evaluated its effectiveness in ameliorating postoperative scars in 17 Mohs surgery patients and compared the results with those seen with a topical emollient. No statistically significant differences were observed between pre- and posttreatment scar erythema and pruritus in the Mederma group, but such differences were found in the group using the petrolatum-based emollient (Dermatol. Surg. 1999;25:267–9).
These relatively small studies are encouraging but hardly definitive. The use of Mederma for hypertrophic scars nevertheless has become prevalent in the clinical setting (Plast. Reconstr. Surg. 2002;110:177–83; discussion 184–6).
Mederma Skin Care for Scars is a topical gel formulated with the proprietary botanical extract blend Cepalin, and is intended to soften and smooth scars such as keloids and striae albae. This greaseless, unscented formulation is designed to be rubbed three or four times a day for 8 weeks into new scars, and for 3–6 months into old scars.
Contractubex, which has been on the market slightly longer, contains cepae extract (derived from onions), heparin, and allantoin and is intended to treat old and recent scars of any origin. This water-soluble gel must be applied several times a day over several months and does not leave a residue. Onion extract is also included in a number of new products intended for scar treatment, such as “derma e.”
The evidence pointing to some pharmacologic activity of onion extract is gaining strength. Nevertheless, there remains a paucity of research supporting the use of onion extract products as a first-line therapy for hypertrophic scars or keloids. Like other botanical products, the use of onion extract in over-the-counter cosmeceutical products will likely continue in spite of the lack of convincing clinical research.
© 2005 Elsevier Inc. All rights reserved.