Galactomyces

Galactomyces ferment filtrate is made by growing a yeast-like fungus in a nutrient broth, then removing the organism and filtering the liquid. The INCI name can cover more than one species of Galactomyces [1]. SK-II calls its version PITERA and describes it as rich in vitamins, amino acids, minerals and organic acids, but it doesn't publish the organism or process [2][3]. In plain terms, it's a watery mix of small molecules that help skin hold water, which fits its hydrating, softening feel.

SK-II's origin story is that scientists in the 1970s noticed elderly sake brewers' hands looked younger than their age and screened 350 yeasts [9]. That's a brand anecdote, not evidence.

Three human studies exist, all small and none placebo-controlled. In a 12-month P&G study, 86 Japanese women using three SK-II products reported smoother texture, fewer visible spots, better hydration and less water loss; there was no control group and every author worked for or consulted to P&G [4]. In an eight-week P&G study, 104 Japanese women aged 22 to 34 used a product with more than 90% galactomyces and saw smaller-looking pores, less roughness and less redness compared with their own four-week baseline [5]. A Korean study of 20 people using a 97% galactomyces essence reported less oil and fewer visible blackheads, but its design, funding and duration aren't clearly described [6].

Tolerability looks good. A US safety panel found galactomyces is used at up to 90.7% in leave-on moisturisers, patch tests on more than 200 people (including an essence at 92.7%) were negative, and it concluded the ingredient is safe as used in cosmetics [1].

Fungal acne is the open question. A dermatologist notes that ferments are deactivated and can't grow on skin, but galactomyces may contain leftover fungal proteins and nutrients that could feed Malassezia, which hasn't been proven; she advises caution for people with a history of fungal acne [7].