Is Onion Extract Effective on Keloid Scars?

Onion extract (Allium cepa) is an active ingredient of many over-the-counter herbal products for scar treatment (e.g., Mederma®).⁵ The primary component in onions is quercetin, a flavonoid known for its potent biological effects.³ Extensive research on scarring suggests that when used by themselves quercetin-containing creams may be far more effective at preventing scars, however, than in treating them after they have already formed.^3,40

How Does Onion Extract Work?

Lab studies show that quercetin inhibits a number of processes that are key to the formation of keloids, and onion extract has demonstrated anti-inflammatory, antibacterial, and collagen-suppressive properties in animal studies.^3,5

In one animal study, application of quercetin cream to skin wounds significantly inhibited the formation of scars compared to the group treated with a placebo. This study revealed that quercetin also exerts an antihistamine effect that appears to help inhibit excess collagen production. Histamine is produced by mast cells, which are involved in the formation of keloids as it significantly stimulates growth of fibroblasts—the cells that produce collagen.⁴⁰

Is Onion Extract Effective on Keloids?

Despite lab and animal study success, human studies on onion extract show mixed results, indicating the need for further research. For example, it failed to demonstrate any benefit in abnormal scar tissue in three human clinical trials.^5,20 However, in later studies onion extract significantly improved the appearance of post-shaving wounds and reduced the incidence of scar development after laser tattoo removal as compared to untreated control groups.³

When combined with other therapies on existing hypertrophic scars and keloids, onion extract seems to improve the effectiveness of those treatments:

• Contractubex® gel (not FDA approved) combines heparin and onion extract; a randomized clinical trial showed that it reduced pain, itchiness, and elevation of keloids more than steroid injections alone.⁴¹
• Improved appearance of inflammation and redness better than silicon sheets by themselves.³
• By itself and in combination with hydrocortisone ointment, silicone, and vitamin E, onion extract produced greater patient satisfaction than placebo treatment.³