Study finds safer skin whitening solution in postbiotic

A study has found that phenyllactic acid (PLA) has skin whitening effects. The results show it significantly inhibits melanin production and cellular tyrosinase activity, potentially making it a safer ingredient in brightening skin care and cosmetic formulations. 

PLA is a metabolite derived from probiotic Limosilactobacillus reuteri (L. reuteri), making it a postbiotic. It inhibits tyrosinase — the primary enzyme that converts amino acids into pigment — and downregulates TRP-1 and TRP-2 — helper enzymes that facilitate the process. 

“Inhibition of tyrosinase activity and TRP expression represents a central strategy in whitening research, with several compounds such as arbutin, kojic acid, and L-ascorbic acid derivatives already commercialized based on this mechanism,” says the study.

In comparison to whitening ingredients such as niacinamide, arbutin, and kojic acid — which lower the master pigment regulator MITF (microphthalmia-associated transcription factor) — PLA increases MITF while still reducing TRP-1 and TRP-2. The researchers say this unusual behavior makes it a novel brightening ingredient for skin care.

It also acts on the second stage of melanin synthesis, making it efficient for stubborn dark spots and pigmentation.

The scientists assert that current products on the market often have limited applications due to side effects such as cytotoxicity, instability, and safety concerns during prolonged use. “These drawbacks underscore the need for alternative whitening agents that exhibit both high efficacy and improved safety profiles.”

Biotics in skin care

The researchers note that probiotics have gained increased attention for dermatological and cosmetic applications in recent years. This is attributed to their eco- and skin-friendly properties.

L. reuteri is a probiotic capable of colonizing various hosts. It naturally lives in multiple parts of the human body’s gastrointestinal tract, urinary tract, breast milk, and on the skin.

The probiotic is already known from previous studies to exhibit benefits such as boosting digestion, supporting the immune system, reducing inflammation, and fighting harmful bacteria.

The new study, published in Cosmetics, found that PLA reduces melanin by blocking key enzymes and by lowering TRP-1 and TRP-2, even though it raises MITF levels — a rare effect compared to typical brightening ingredients.

The researchers expect PLA to be suitable for formulations such as essences or toners.“PLA exhibits whitening effects equivalent to or greater than arbutin without cytotoxicity by competitively inhibiting tyrosinase and selectively inhibiting the expression of genes related to melanin production,” says the study.

The results suggest that PLA is a promising candidate for safe and effective skin whitening ingredients in functional cosmetics, due to its low toxicity. 

PLA is water-soluble and expected to remain stable in mildly acidic environments. This makes it suitable for formulations such as essences or toners. 

The researchers note that further studies are needed to optimize formulation stability.

Toxic alternatives

The study comes amid growing concerns about the safety of skin-whitening products, with some containing mercury. 

Personal Care Insights recently spoke to Zero Mercury Working Group about governments agreeing on a global plan to crack down on cosmetics containing mercury at COP-6. The organization representative called the sale of mercury-added cosmetics “a vast global criminal enterprise.” 

Mercury can be regarded as an appealing ingredient to add to skin-lightening, brightening, and bleaching cosmetics due to its fast-acting efficacy. The neurotoxin inhibits melanin production, making the skin appear fairer within days.

A previous study revealed that 22 out of 26 popular skin-lightening creams sold in Bangladesh contain mercury levels up to 24,800 times the legal limit, violating international treaty commitments and national bans.

Last year, the EcoWaste Coalition flagged skin-lightening products containing mercury after conducting a series of test purchases in Pasay City, Philippines. The coalition uncovered the illegal sale of imported products with mercury content ranging from 11,940 to 28,370 parts per million.

These toxic products are driving science to look for alternatives. A recent study found promising results from turmeric. Turmeric is an antioxidant that fights oxidative stress caused by UV exposure and pollution. This helps against hyperpigmentation and aging, and the researchers argue that turmeric could protect the skin from forming new dark spots while reducing inflammation.