Preservatives, a chemicals that we are all afraid of. Are they as harmful as many of us think and do we really need them in cosmetics? Today I would like to write about the role of different preservatives in skin care formulations and about their influence on the skin and the skin microbiome. About skin microbiome you could read already on my blog earlier.
As you all could imagine, cosmetics containing large amounts of water and organic ingredients are extremely susceptible to action of microbes. Imagine all of the oils, proteins and sugars in your moist cosmetics. Yes, this is a perfect environment for growth of different bacteria (Staphylococcus aureus, Pseudomonas aeruginosa) and fungi (Candida albicans). Unprotected cosmetics have a fairly short period of safe use, which can vary from few days up to a few weeks. Microorganisms produce different metabolites, which can affect color, smell and composition of cosmetics. Many of these metabolites are very harmful for us. Microbes in cosmetics lead to change of their physical properties and can be a real danger for our skin, leading to inflammation, infection and allergies. How do the cosmetic companies fight that problem out? Here come the preservatives into the game. After applying an appropriate preservative system, each cosmetic product can be used without any problems for up to 6 months after opening.
What actually are these preservatives – these are all substances which are able to stop or strongly reduce a bacterial and fungal growth in different products. They are constantly used to prevent microbial growth in our foods. Do not confuse them with antibiotics. Antibiotics as a prescription drugs can’t be used as a preservatives. Bacteria and fungi are pretty smart in developing resistance to antibiotics, what in the future could lead to development of antibiotic resistance to all of antibiotics that we know. That would be a disaster for a man kind. Preservatives have a toxic effect on all (or most of microorganisms). In cosmetics we can use them in a very low concentrations- enough to stop bacterial and fungal growth and not to harm our organisms.
Are they really safe for us? Actually yes, each cosmetic before it is approved for sale has to undergo many tests to evaluate its safety, so as not to endanger the health of the person that will use it. Each of formulations has to undergo many dermatological and microbiological tests, cosmetic durability and efficacy tests as well. However, despite all of these investigations, different skin reactions (allergies and skin irritations cannot be excluded). Due to the widespread use of cosmetics and way more immunity problems among our population than ever, allergic reactions and cosmetic-associated irritations are more and more often observed. The composition of cosmetic products is very rich, what makes it very difficult to determine which of the components is an allergenic factor. Although we cannot avoid use of preservatives in cosmetic formulation, there are some of them which are safe and really worth to write about. They do not only preserve products from harmful microorganisms, sometimes they have even a very positive influence on the skin and skin microbiome.
Which preservatives should you avoid in your cosmetic products and which of them you can for sure apply on your skin? Lets start with the most popular ones: phenoxyethanol and ethylhexylglycerin.
Phenoxyethanol
Phenoxyethanol (2-phenoxyethanol) is a preservative that is commonly found in skin care cosmetics. Some time ago there was a lot of talk about it. Is it good? Is it bad? Does it harm the skin? Does it lead to occurrence of allergic reactions? In cosmetics, it is present mainly in creams, lotions and other preparations for moisturizing the skin of the body, including the face. Phenoxyethanol is allowed to be used in cosmetics in a limited concentration (up to 1%). It is effective against a variety of gram-negative and gram-positive bacteria as well as yeasts and has only a weak inhibitory effect on the skin flora. It has a very nice smell and is a great solvent for many chemicals. Although it is a very safe preservative, people with very sensitive skin type should avoid it in their daily skin care routine. It is allergenic substance capable of causing numerous unpleasant irritations and allergic skin lesions. For this reason, cosmetics with phenoxyethanol should not be used by people with very sensitive skin and people suffering from skin diseases (psoriasis and atopic dermatitis).
Ethylhexylglycerin
Ethylhexylglycerin is a glycerin (a carbohydrate belonging to polyols – sugar alcohol) derivative. Ethylhexylglycerin is a liquid substance and has no color under normal conditions (room temperature, normal pressure). It dissolves well in water and oil solutions. It has a very strong preservative properties and acts against yeast and bacteria. It is a humectant as well, what means that it can bind water and shows moisturizing properties. It can enhance action of other preservatives, therefor very often we can find it in cosmetic formulations together with phenoxyethanol. Ethylhexylglycerin reduces the unpleasant smell on the skin as well. It does not disrupt the natural lipid layer of the skin, what makes it one of the safest cosmetic preservatives. It does not show any allergenic or irritating effect. It can be safely used by women during pregnancy and breastfeeding. In some sources we can find information that ethylhexylglycerin is a compound that can irritate the eye area in very high concentrations, what actually doesn’t apply to cosmetic products, as it is used there in a very low amount.
For all of the people, that are afraid of (or have allergy to) phenoxyethanol and ethylhexylglycerin I would like to give few another safe preservatives which you could pay attention to. These could be sodium benzoate, potassium sorbate, pentylene glycol and bacterial ferments.
Sodium benzoate
Sodium Benzoate is a traditional preservative that is used extensively in the cosmetics, food and pharmaceutical industries. It protects effectively against the growth of microorganisms like fungi and bacteria. It belongs to very safe preservatives and it is approved for use in ecological cosmetics. Sodium benzoate is the sodium salt of benzoic acid, which is known to have very strong antimicrobial properties as well. The recommended concentration in the cosmetic products is 0.2% to 0.4%. Some people can claim that due to possible conversion to benzoate it should be classified as harmful, however such reaction can take place only in combination with ascorbic acid in the presence of different physical and chemical factors such as metal ions and UV radiation (therefore sometimes you can find information, that it should be avoided in formulations containing vitamin C). Although there is such a possibility, amount of created benzoate would be so low, that use of sodium benzoate in cosmetics is completely safe.
Potassium sorbate
Similarly to sodium benzoate, potassium sorbate is a traditional preservative used in the cosmetics and food industries as well. It effectively reduces the growth of yeast and bacteria, with the exception of beneficial lactic acid bacteria (what makes it skin microbiome friendly). Potassium Sorbate is the potassium salt of sorbic acid that occurs naturally in the fruits of rowan (Sorbus aucuparia). Similarly to sodium benzoate, the recommended concentration in the cosmetic product is 0.2% to 0.4%.
Pentylene glycol
Glycols belong to the group of alcohols, an extremely wide and diverse group of organic compounds. Glycols, similarly to popular alcohols, like ethanol and methanol also have an -OH (hydroxyl group) molecule attached to the hydrocarbon chain, more precisely they belong to diols (they have two hydroxyl groups bound to hydrocarbon chain). Ethylhyxylglycerin, which is a derivative of glycerol is a diol as well (it hast wo -OH groups as well). Pentylene glycol can be easily used as an alternative preservative, because the concentration at which it achieves its antimicrobial properties is around 5%. Its chemical structure lets it to dissolve well in water. It has ability to penetrate to stratum corneum and to enhance transport of active substances into the skin. Apart from that it has very strong moisturizing properties as well. It is great preservative that softens and maintains the skin in a good condition. The compound is not genotoxic and does not cause skin irritation or allergy. As a Humectant it additionally prevents the cosmetic preparation from drying out and crystallization.
Lactobacillus ferment:
Lactobacillus is a type of bacteria that naturally lives on the surface of our skin and is used to ferment food such as yoghurt, kefir and sauerkraut. Lactobacillus ferment in cosmetology, can be used as an antimicrobial agent, providing a broad spectrum of antibacterial activity. It is a safe alternative to other controversial preservatives. It is very effective against pathogenic bacteria and yeast (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans). Many researchers showed so far, that apart of its antimicrobial properties, it also has a moisturizing effect and can stimulate growth of friendly skin bacteria (acts as an prebiotic). Addition of 2% Lactobacillus ferment into the cosmetic formulation led to an improvement in skin hydration by about 15 – 25% after four weeks.
Leuconostoc / radish root ferment filtrate
Leuconostoc / radish root ferment filtrate is a natural preservative of plant origin based on antibacterial peptides that are produced in the fermentation of radish (Raphanus sativus) by human-friendly lactic acid bacteria of the genus Leuconostoc kimchii. It is skin-friendly and became great alternative to traditional, synthetic preservatives (phenoxyethanol). Similarly to Lactobacillus ferment, it protects the cosmetic preparations against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Klebsiella pneumoniae, Bulkholderia cepacia. It hydrates the skin and stimulates growth of skin microbiome. When used in a concentration of only 1%, it increases the level of skin hydration by more than 10%.
Impact of preservatives on skin microbiome
On our skin there is a community of billions of different bacteria per square centimeter! This community is called skin microbiome. Similarly to gut microbiome, on the skin we can find diverse strains of lactic acid bacteria and yeast. Most common are Propionibacterium, Corynebacterium, Lactobacillus, Staphylococci and Bifidobacterium. They reside on our skin from our birth and have very important protective function for our organism. Does use of preservatives impact skin microbiome?
As many scientific investigations show, use of preservatives in cosmetic formulations do not really necessarily have to influence skin microbiota. A very interesting paper showed that different preservation systems used in cosmetics (either used for washing or in creams) do not influence skin microbiome. The investigation have been carried out through 5 weeks and didn’t show much of change in diversity of skin bacteria. This was actually in line with similar studies, which focused on using soap for washing the hands. Although soap led to slight alternations in skin microbiome, these were only short-term changes and bacteria could easily recover (however, remember that soap alternates hydrolipid barrier of the skin). However all of the research have been conducted only for a low period of time, therefor it is important to get some more information about influence of such cosmetic use for longer time. Another interesting study examined influence on the skin of preservative formulation with and without high molecular weight inulin- a very popular prebiotic. What was the outcome of this research? The use of preservative formulation without prebiotic led to drastic decrease of microorganism population after 2 hours of cosmetic application. 50% of bacteria recovered after 4 hours, however one has to think that that formulation was a pretty hardcore for skin microbiome – it contained phanoxyethanol, diazolinidyl urea, methyl and propyl parabens and propylene glycol. Application of cosmetics with inulin had an outstanding result on skin bacteria. Despite very high concentration of preservative, these cosmetics led to total recovery of skin microbiome after 4 hours. Moreover, it has been shown, that they enhanced skin hydration by 22% in comparison to control formulation, which contained 0.1% hyaluronic acid as hydrating agent.
As you can see, preservatives are really not that bad in cosmetic formulations! From my side, I would advise you to look for cosmetics with prebiotics (inulin, bacterial ferments, yeast ferments, glucan) rather than give up on cosmetics because there is a common preservative in its formulation. If you are really afraid of preservatives, choose products with ethylhexylglycerin, penthylene glycol or bacterial ferments 🙂
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