Ingredient review

Fermented Horsetail & Soybean Complex

INCI: BACILLUS/MONASCUS/EQUISETUM ARVENSE LEAF/SOYBEAN SEED FERMENT FILTRATE

A fermented botanical complex that may offer antioxidant and skin-soothing benefits, but research is still emerging.

beautyskincareantioxidantconditioning agent

In plain English

This ingredient is made by fermenting horsetail leaf and soybean seeds with beneficial bacteria and yeast. The fermentation process breaks down the plant materials into smaller, potentially more absorbable compounds. It's used in skincare for its antioxidant properties (helping protect skin from environmental damage) and as a gentle skin conditioner. Think of it as a plant-based probiotic tea for your skin.

Quick decision guide

Useful, but context matters

Fermented Horsetail & Soybean Complex is generally a lower-concern ingredient when the full formula suits your skin.

Plain-English read

Treat this as a practical screening step before you compare products that contain this ingredient.

  1. Step 1Start with the score, then check the irritation and clogging risk before judging Fermented Horsetail & Soybean Complex.
  2. Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
  3. Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.

Score terms in plain English

Irritation risk

low

Less likely to sting, burn, or bother most users, though sensitive skin can still react.

Clogging risk

low

Less likely to feel heavy or contribute to clogged pores for most skin types.

Evidence level

emerging

The ingredient may be promising, but claims should be treated more cautiously.

What it is

A fermentation filtrate created by culturing Bacillus and Monascus microorganisms on a mixture of horsetail (Equisetum arvense) leaf and soybean (Glycine max) seed. The resulting liquid is filtered and used as a skincare ingredient rich in peptides, amino acids, and plant-derived antioxidants.

How it works

During fermentation, microorganisms break down plant proteins and carbohydrates into smaller peptides, amino acids, and sugars. These smaller molecules can more easily interact with the skin's surface, potentially providing antioxidant protection (neutralizing free radicals) and supporting the skin's natural moisture barrier. The filtrate may also contain enzymes and metabolites that gently exfoliate or condition the skin.

Pros

Antioxidant potential

The fermentation process may boost the bioavailability of antioxidant compounds from horsetail and soybean, helping protect skin from environmental stressors like pollution and UV damage.

Gentle conditioning

As a fermented filtrate, it's generally mild and can provide light hydration and skin softening without heavy oils or synthetic thickeners, making it suitable for daily use.

Cons and cautions

Limited evidence

Most benefits are based on the known properties of the source plants and fermentation in general, not on direct clinical studies of this specific filtrate. Results may vary.

Potential allergen risk

Soy is a common allergen, and horsetail may cause reactions in some individuals. Always patch test before widespread use, especially if you have plant allergies.

Best for

  • Those looking for antioxidant-rich, fermented skincare
  • People with normal to dry skin seeking gentle conditioning
  • Fans of K-beauty style fermented essences

Use caution if

  • Individuals with known allergies to soy or horsetail
  • Those with very sensitive skin who react to fermented ingredients (patch test first)

Usage tips

Apply after cleansing and before heavier creams to allow the filtrate to absorb.
Store in a cool, dark place to preserve the stability of the fermented compounds.
Use consistently over several weeks to assess any cumulative benefits.

Safety summary

This ingredient is considered safe for topical cosmetic use at typical concentrations. The main risks are allergic reactions in individuals sensitive to soy or horsetail. As with any fermented ingredient, proper preservation in the final product is important to prevent microbial contamination.

Research notes

Research on this specific ferment filtrate is limited. However, studies on fermented plant extracts generally show enhanced antioxidant activity and improved skin penetration of active compounds. Horsetail is known for its antioxidant and anti-inflammatory properties, while soybean ferments are studied for skin brightening and barrier support. More direct human trials are needed.

Common label clues

Typical concentration
Typically 1–10% in leave-on products
Regulatory status
Generally recognized as safe for cosmetic use in the US and EU when used as intended. No specific restrictions beyond standard cosmetic ingredient regulations.
Common uses
Serums, Essences, Moisturizers, Toner
Environmental note
Fermentation is a relatively low-energy, bio-based process. Soybean sourcing may raise sustainability concerns depending on agricultural practices; look for brands that disclose sourcing.

Good to know

  • Fermented ingredients are popular in Asian beauty routines for their perceived gentle efficacy.
  • The specific strains of Bacillus and Monascus used can influence the final composition of the filtrate.

Common questions

What is Fermented Horsetail & Soybean Complex in beauty products?

This ingredient is made by fermenting horsetail leaf and soybean seeds with beneficial bacteria and yeast. The fermentation process breaks down the plant materials into smaller, potentially more absorbable compounds. It's used in skincare for its antioxidant properties (helping protect skin from environmental damage) and as a gentle skin conditioner. Think of it as a plant-based probiotic tea for your skin.

What does Fermented Horsetail & Soybean Complex do in a beauty product?

During fermentation, microorganisms break down plant proteins and carbohydrates into smaller peptides, amino acids, and sugars. These smaller molecules can more easily interact with the skin's surface, potentially providing antioxidant protection (neutralizing free radicals) and supporting the skin's natural moisture barrier. The filtrate may also contain enzymes and metabolites that gently exfoliate or condition the skin.

Is Fermented Horsetail & Soybean Complex safe for most people?

This ingredient is considered safe for topical cosmetic use at typical concentrations. The main risks are allergic reactions in individuals sensitive to soy or horsetail. As with any fermented ingredient, proper preservation in the final product is important to prevent microbial contamination.

Who should be careful with Fermented Horsetail & Soybean Complex?

Individuals with known allergies to soy or horsetail Those with very sensitive skin who react to fermented ingredients (patch test first)

Research sources

INCI Database - SpecialChemOpenPubMed - Fermented Plant Extracts in CosmeticsOpenCosmetic Ingredient Review (CIR) - Safety of Ferment FiltratesOpen

Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.