Polylysine: What Is It, Hair Benefits & Side Effects

Priya Singh
Fact-Checker: Priya Singh
This article was last updated on: November 20, 2023
Table of Contents

Navigating the world of personal care and cosmetic products, whether skincare or hair care, can often feel like deciphering a cryptic code. The ingredients listed on the packaging are usually a mix of familiar and utterly foreign terms, making it challenging for anyone without a background in cosmetic science to understand what they’re applying to their skin and hair. This complexity can sometimes make choosing the right product feel like a gamble.

This article aims to shed light on the cosmetic use of Polylysine. We will delve into its origins, how it functions, potential side effects, and why it’s used in cosmetic formulations!

What is Polylysine?

Polylysine, scientifically referred to as Poly(imino-(6-amino-1-oxo-2,1-hexanediyl), .alpha.-hydro-.omega.-hydroxy-, is a unique ingredient in the cosmetic world. It’s not as ubiquitous as some other components, but it holds its own in hair care products. This ingredient may also be known under different names in various formulations, but ‘Polylysine’ remains its most recognized label.

In cosmetics, Polylysine primarily serves as a hair conditioning agent. Its function is to enhance the appearance and feel of hair, by improving hair texture, providing moisture, and generally making hair easier to comb and manage. The way Polylysine works is by forming a thin, coating layer on the hair shaft. This coating not only smoothens the hair but also provides a protective barrier, which can help in reducing hair damage from environmental stressors.

The concentration of Polylysine in cosmetic products varies, but it’s typically used in small percentages (around 0.1-2%); this is because even at low concentrations, it’s effective in delivering its conditioning benefits.

Who Can Use Polylysine?

Polylysine is a versatile ingredient suitable for a wide range of skin types. It’s particularly beneficial for those looking to enhance the health and appearance of their hair. Due to its gentle nature, Polylysine is generally well-tolerated by most skin and hair types, making it a suitable option for people with various hair concerns.

For those conscious about animal-derived ingredients, Polylysine is an ingredient to take note of. Its chemical composition suggests that it is suitable for vegans and vegetarians, but it’s always wise to check the full ingredient list of a product for any hidden animal-derived components.

When it comes to use by women who are pregnant or breastfeeding, there’s no specific indication that Polylysine poses any risks. However, as with any cosmetic ingredient, it’s recommended that pregnant or breastfeeding women consult with a healthcare provider before incorporating new products into their routine. This precaution ensures that they’re making the safest choices for both themselves and their children.

Polylysine Hair Benefits

Polylysine offers several benefits for hair:

  • Enhanced Hair Smoothness: Polylysine’s ability to enhance hair smoothness is one of its standout benefits. It forms a thin, protective layer over the hair strands. This layer effectively smooths out the surface of the hair, significantly reducing frizz and making the hair feel silkier and more manageable. The smooth surface of the hair also better reflects light, which can enhance the natural shine of the hair. This benefit is not just a temporary fix; with regular use, Polylysine can progressively improve the hair’s texture, leading to long-term smoothness.
  • Improved Hair Manageability: The impact of Polylysine on hair manageability is especially beneficial. Smoothing down the hair cuticles makes detangling a breeze, substantially reducing the effort required in combing and styling. This is particularly advantageous for those with longer or curlier hair types, where tangling is a frequent challenge. The ease of managing hair that Polylysine provides can be a significant time-saver and reduce hair damage caused by excessive pulling and brushing.
  • Hydration Retention: Hydration is key to healthy hair, and Polylysine plays a vital role in maintaining this balance. By forming a barrier around the hair, it helps in minimizing moisture loss, thus keeping the hair hydrated for extended periods. Well-hydrated hair is less prone to breakage and generally looks healthier and more vibrant. This benefit of Polylysine is crucial for those who struggle with dry and brittle hair, as it aids in maintaining the hair’s natural moisture.
  • Protection Against Environmental Stressors: The protective layer provided by Polylysine also offers a shield against environmental damage such as UV rays, pollution, and humidity. This protection is crucial for maintaining hair health, as it helps in preserving the hair’s natural color and texture, especially important for treated or colored hair. By guarding against these external factors, Polylysine helps in keeping the hair in its optimal condition.

It’s important to remember that the benefits of polylysine are maintained through consistent use. Its protective and conditioning effects are not permanent and require regular application as part of a hair care routine.

Polylysine Potential Side Effects

While Polylysine is generally considered safe for cosmetic products, reactions can vary from person to person. This variance in response is due to individual differences in skin type, existing allergies, and sensitivities. Genetic predisposition, environmental influences, and overall skin health can also play a role. Understanding your skin type is crucial in predicting how your skin might react to certain ingredients.

Potential side effects and interactions with Polylysine, although rare, might include:

  • Skin Irritation: Some individuals might experience redness, itching, or slight swelling on the skin where the product is applied.
  • Allergic Reactions: In rare cases, an allergic reaction could occur, especially in individuals with a history of allergies to cosmetic ingredients.
  • Hair Dryness: Overuse of products containing Polylysine might lead to hair dryness in some cases, as the protective layer it forms can potentially reduce hair’s natural moisture over time.

If you experience any of these side effects while using a product containing Polylysine, it is advisable to discontinue use immediately and consult a dermatologist or healthcare provider. They can provide guidance and, if necessary, suggest alternative products that might be more suitable for your skin or hair type.

Despite these potential side effects, it’s important to note that adverse reactions to Polylysine are rare. The ingredient is generally well-tolerated and effective for its intended use in hair conditioning. However, as with any cosmetic ingredient, individual experiences can vary.

To minimize the risk of adverse reactions, it is essential to conduct a patch test before incorporating a new product into your routine. A patch test helps determine how your skin will react to the product. For a detailed guide on how to conduct a patch test, refer to our patch testing guide.

Comedogenic Rating

When it comes to the comedogenic rating of Polylysine, it can be rated as 0/5, indicating that it is non-comedogenic. This rating means that Polylysine is unlikely to clog pores or exacerbate acne issues.

Polylysine’s molecular structure and function in hair care products suggest that it does not contribute to the blockage of hair follicles, which is a primary cause of comedones (pimples). Therefore, for those prone to acne or breakouts on the scalp, Polylysine can be considered a safe ingredient to use in hair care products.


Success in hair care often boils down to a blend of experimentation, trial and error, and maintaining consistency once you discover what works for your hair. Every individual’s hair is unique, and what may be effective for one person might not yield the same results for another. Polylysine, with its specific benefits for hair conditioning, represents one of many options in the vast world of hair care ingredients.

Opting for products containing Polylysine may be beneficial for those seeking improved hair manageability, smoothness, and protection against environmental stressors. It’s an ingredient that might not be as well-known or as popular as some others, but its efficacy in hair conditioning cannot be understated. Polylysine is not a common ingredient in hair care formulations, but when it is used, it’s appreciated for its specific benefits. It shares similarities with other conditioning agents, although its unique properties set it apart.

In terms of seeing results from polylysine, they vary from individual to individual. Some might notice improvements in hair texture and manageability relatively quickly, while for others, it might take consistent use over a more extended period to observe significant changes.

If you have concerns about using Polylysine in your hair care regimen, it’s important to remember that adverse reactions are rare, and its non-comedogenic nature makes it suitable for a wide range of hair types. Its specific role in improving hair health and appearance can make it a valuable addition to your hair care routine, especially if you’re exploring options to enhance your hair’s overall condition.

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