Onion Extract

Overview

Onion extract is made from the bulb of the common onion (Allium cepa) — yes, the kitchen onion. It came to cosmetic prominence through a specific product category: scar gels. Several clinical studies in the 1990s and 2000s showed that onion extract gels (typically combined with allantoin and heparin) modestly improved the appearance of raised, red, hypertrophic, and keloid scars over months of consistent use. That clinical pedigree is unusual for a kitchen-derived extract.

The chemistry includes quercetin (a major flavonoid), other flavonoids, sulfur-containing compounds (the chemistry of the famous onion-tear effect), and various polysaccharides. The quercetin is widely credited with the anti-inflammatory and capillary-supporting effects.

In DIY supply, onion extract comes as:

• Hydroglycerinated liquid extract (most common, water-soluble, pale yellow)
• Standardized quercetin extract
• Onion juice (less concentrated, occasionally used)

The cosmetic-grade extract is deodorized — without this, the onion scent would dominate the entire formula. Even so, sensitive noses can sometimes detect a faint allium character.

Shelf life is 1-2 years for liquid forms stored cool and dark.

What it does in a formula

The quercetin and flavonoid content delivers:

• Scar improvement — particularly for raised, red, hypertrophic, and keloid scars
• Anti-inflammatory — useful for rosacea and reactive skin
• Antibacterial — surface action of sulfur compounds
• Capillary support — quercetin strengthens capillary walls
• Antioxidant — broad polyphenol activity
• Hair scalp benefits — folk claim of supporting hair growth (modest evidence, mostly from oral or topical concentrated extracts, not from cosmetic concentrations)

The scar-improvement evidence base is the most distinctive aspect. Combined with allantoin and heparin, onion extract has been used in clinically-positioned scar products for decades.

How to use

Add to the water phase. Tolerates heat-and-hold to 80 C.

Usage rates by product type (hydroglycerinated extract):

• Scar gels: 10-15%
• Stretch-mark creams: 5-10%
• Post-surgical scar creams (cosmetic): 5-15%
• Anti-inflammatory face creams: 2-5%
• Hair scalp tonics: 3-5%
• Burn aftercare: 5-10%

For scar gels following the classic clinical formulation, pair with 0.5% allantoin and 0.1% heparin sodium (heparin is restricted in some markets — check rules).

Best for / Worst for

Best for: scar gels and creams, hypertrophic and keloid scar fading, post-surgical cosmetic recovery, stretch-mark creams, hair scalp tonics, anti-inflammatory formulas wanting clinical pedigree.

Worst for: perfume-clean formulas (faint allium scent), customers with allium allergies (rare but exist), customers expecting fast visible scar fading (it is slow — months of consistent use), strict natural-fragrance brands.

Common pitfalls

Onion scent breakthrough. Even deodorized onion extract can show through in formulas with subtle fragrance. Pair with complementary scent notes (rosemary, lavender, neutral oils).

Slow results. Scar improvement takes 3-6 months of consistent use. Set customer expectations.

Overpromising new scars. Onion extract works best on raised scars in the active healing-then-remodeling phase. Old, fully matured scars respond less.

Fresh keloids and active wounds. Onion gel should not be applied to fresh wounds. Wait until the wound has closed.

Allium family allergy. Cross-reactivity with garlic, leek, and other alliums is possible.

Heparin pairing. The classic scar-gel formulation uses heparin, which is restricted in some markets and animal-derived. Vegan formulas omit heparin.

Substitutes

• Centella asiatica titrated extract — broader scar fading, vegan.
• Allantoin — wound-healing alternative, gentler.
• Silicone scar sheets / gels — non-botanical clinical alternative.
• Rosehip oil — fellow scar-fading folk use.
• Bakuchiol — gentle anti-aging, modest scar support.
• Madecassoside — isolated centella active for clinical positioning.