Lactobacillus, yeast, and koji — types and differences of fermented ingredients

Many cosmetics are labeled "contains fermented ingredients," but the microorganisms used for fermentation produce completely different compounds and effects. Here we compare the four main types of fermented ingredients.

1. Lactic acid bacteria ferment

Lactic acid bacteria (Lactobacillus, etc.) produce lactic acid and short-chain fatty acids that maintain the skin's mildly acidic pH and strengthen barrier function. They also excel at moisturizing and are commonly used in products for sensitive skin.

2. Yeast extract / Galactomyces culture filtrate

Yeast culture filtrates (Saccharomyces, Galactomyces, etc.) are rich in B vitamins, minerals, and amino acids. They help regulate skin turnover and promote radiance. Famous as the main ingredient in Korean cosmetics' "first treatment essences."

3. Koji / Rice ferment filtrate

Rice fermented by koji mold (Aspergillus oryzae) produces kojic acid. Kojic acid inhibits tyrosinase (melanin synthesis enzyme) and is an approved active brightening ingredient in quasi-drugs. This is why sake brewers' hands are so beautiful.

4. Bacillus ferment

Fermented products derived from Bacillus subtilis contain proteases (protein-degrading enzymes) that provide gentle exfoliation. They are less irritating than chemical peeling and enable mild keratin removal.

As you can see, even under the umbrella of "fermented ingredients," the effects differ significantly depending on the type of microorganism. Choosing fermented ingredients that match your skin concerns is the first step to effective skincare.