Ingredient review
Polylysine
INCI: POLYLYSINE
A gentle, naturally-derived preservative booster that helps keep your skincare products fresh without harsh chemicals.
In plain English
Polylysine is a natural substance made by fermenting a specific type of bacteria. It acts like a gentle bodyguard for your skincare products, stopping bacteria, yeast, and mold from growing. This helps your lotions and creams stay safe to use longer. It's often used alongside other preservatives to reduce the need for stronger synthetic ones.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- biotech
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Polylysine 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.
- Step 1Start with the score, then check the irritation and clogging risk before judging Polylysine.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- 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
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
Polylysine is a small protein (a chain of the amino acid lysine) produced through fermentation of the bacterium *Streptomyces albulus*. It is a natural antimicrobial peptide used in cosmetics to inhibit the growth of microorganisms.
How it works
Polylysine works by disrupting the cell membranes of bacteria, yeast, and mold. It binds to the negatively charged surfaces of these microbes, causing their membranes to leak and eventually killing them. This action helps preserve the product without affecting your skin cells.
Pros
Naturally derived
Made through fermentation, polylysine appeals to those seeking more natural or 'clean' beauty options without sacrificing product safety.
Low irritation potential
Unlike some synthetic preservatives, polylysine is very gentle on skin and rarely causes stinging or allergic reactions, making it suitable for sensitive skin formulas.
Cons and cautions
Not a standalone preservative
Polylysine is typically used as a booster in a preservative system, not alone. It works best with other preservatives to fully protect the product from all types of microbes.
pH sensitive
Its antimicrobial activity is strongest in slightly acidic to neutral pH (around 4–7). In very alkaline formulas, its effectiveness drops significantly.
Best for
- Anyone looking for products with a more natural preservative system
- People with sensitive skin who react to traditional preservatives like parabens or formaldehyde releasers
Use caution if
- Those with known allergies to fermented ingredients (rare)
- Formulations that require a very high pH (above 8)
Usage tips
Safety summary
Polylysine is considered safe for use in cosmetics at typical concentrations. It has a low irritation and sensitization potential, making it a gentle alternative to harsher preservatives. Patch testing is always recommended for new products.
Research notes
Research supports polylysine's effectiveness as an antimicrobial agent against a range of bacteria, yeast, and mold. Studies show it is safe for topical use and does not penetrate healthy skin in significant amounts. More research is ongoing to optimize its use in complex cosmetic formulations.
Common label clues
- Typical concentration
- 0.1% to 1%
- Regulatory status
- Approved for use in cosmetics in the EU, USA, and many other regions. In the US, it is generally recognized as safe (GRAS) for food use and is accepted as a cosmetic ingredient.
- Common uses
- Preservative systems, Water-based formulas, Leave-on and rinse-off products
- Environmental note
- Polylysine is produced via fermentation, a relatively low-impact biotech process. It is biodegradable and does not accumulate in the environment.
Good to know
- Polylysine is also used in the food industry as a natural preservative.
- It is biodegradable and considered environmentally friendly.
Common questions
What is Polylysine in beauty products?
Polylysine is a natural substance made by fermenting a specific type of bacteria. It acts like a gentle bodyguard for your skincare products, stopping bacteria, yeast, and mold from growing. This helps your lotions and creams stay safe to use longer. It's often used alongside other preservatives to reduce the need for stronger synthetic ones.
What does Polylysine do in a beauty product?
Polylysine works by disrupting the cell membranes of bacteria, yeast, and mold. It binds to the negatively charged surfaces of these microbes, causing their membranes to leak and eventually killing them. This action helps preserve the product without affecting your skin cells.
Is Polylysine safe for most people?
Polylysine is considered safe for use in cosmetics at typical concentrations. It has a low irritation and sensitization potential, making it a gentle alternative to harsher preservatives. Patch testing is always recommended for new products.
Who should be careful with Polylysine?
Those with known allergies to fermented ingredients (rare) Formulations that require a very high pH (above 8)
Research sources
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.