This new thread was started to answer some questions from Jina (see below) about commonly used cosmetic preservatives. Because Jina is not one to shy away from deeper levels of scientific evidence, I thought we would try something different here. I am going to collect some of the most recent published scientific literature on the substances in question, and either link to it or paste in some abstracts (I cannot give you the whole article as they are copyrighted). l may annotate the abstracts, and give you my brief perspective on what they say. I would appreciate feedback from you readers in terms of whether this is too deep or what.
The first substance to discuss is Phenoxyethanol (PE). It is a commonly used preservative, and was originally touted as the replacement for formaldehye (which is quite toxic). It has replaced formaldehyde in medical pathology labs (preserving cadavers, samples, etc).
The problem is stated as sensitivity and toxicity which are two different things. Toxicity has to do with inherent properties of the chemical e.g. it’s propensity to cause damage to cells, at the DNA level, metabolic, or some other mechanism. Sensitivity has to do with your immune system having decided that this substance is an enemy, whether it is inherently toxic or not. Your skin can become sensitive to otherwise nontoxic molecules (e.g. pollens) which makes it quite problematic for you, but not for everybody. Proteins are especially prone to cause sensitivities or allergies, but any chemical can be sensitizing. Very sensitive people (we call them atopic in the allergy realm) can be easily sensitized to any number of chemicals. But even non-atopic people can be sensitized to chemicals like preservatives by seeing them over and over again.
The problem with Phenoxyethanol is that is is present in so many skin care products. One of the abstracts below (#1) shows it in 3541 “leave on products” Lots of opportunities to be exposed. If you are a skin care “junkie” you may be seeing this substance more often than you think.
Dosing is also important, especially for toxicity. The “acceptable range” (FDA-speak) of concentrations is quite large. Interestingly, it is effective in doses low as 1/20th of the allowed. (#2). For hypersensitive skin, even low concentrations could be a problem, but lower dosing would help a lot.
So, what about toxicity. Abstract #3 below is hot off the press. PE was tested along with two different parabens, benzyl alcohol, and ethylhexyl glycerine. At concentrations of 1% (quite high) cytotoxicity and genotoxicity (DNA alteration) was present for all, with parabens being worse than PE for genotoxicity. Again, higher concentrations than you would normally see in a product. But it does tell us that these chemicals are not without risks.
My own take on this is that PE has a reasonably low risk profile (compared e.g. to parabens) at usual product concentrations, but that lowering concentrations further would be a quite good thing. But, for anyone who thinks they are sensitive to PE, you need to be aware of just how ubiquitous it is these days. Beware that not every chemical in the bottle is on the label.
I am considering a totally “preservative free” version of a product line we are working on. But, you would have to keep it refrigerated to maintain its sterility. It would arrive in a dry ice package. Would there be enough sensitive users out there willing to put up with that inconvenience? Please tell me what you think.
Contact Dermatitis. 2011 Sep;65(3):167-74
Risk of sensitization to preservatives estimated on the basis of patch test data and exposure, according to a sample of 3541 leave-on products.
Schnuch A, Mildau G, Kratz EM, Uter W.
The risk of sensitization cannot be derived from the frequency of sensitization to allergens alone, but exposure should be considered.
To estimate the risk of sensitization to selected preservatives.
The occurrence of preservatives in 3541 leave-on products based on the labelling of the ingredients was documented. Frequency of sensitization to preservatives was analysed on the basis of Information Network of Departments of Dermatology data for 2006-2009. As an estimate of sensitization risk, the sensitization exposure quotient (SEQ) was calculated as the quotient of the relative frequency of sensitization and the relative frequency of use.
The SEQs varied greatly, offering a ranking regarding risk of sensitization: phenoxyethanol (SEQ: 0.06), benzyl alcohol (0.30), parabens (0.35), sorbates (0.92), benzoates (1.35), formaldehyde-releasers (1.6), methylisothiazolinone (MI) (1.7), iodopropynyl butylcarbamate (3.4), methylchloroisothiazolinone/MI (9.0), and 2-bromo-2-nitropropane-1,3-diol (13). There was a good correlation between the ranking of substances according to potency (hazard) and the ranking of the SEQ (risk).
High frequencies of sensitization may be put into perspective by the frequent use of certain preservatives. Despite infrequent use, others (with higher potencies or too high use concentrations) may turn out to be associated with an increased risk. Hazard assessment should be supplemented by risk assessment.
Int J Cosmet Sci. 2011 Apr;33(2):190-
Low-level efficacy of cosmetic preservatives.
Lundov MD, Johansen JD, Zachariae C, Moesby L.
Preservation using combinations of preservatives has several advantages. This study shows that the concentration of some of the most frequently used allergenic preservatives can be markedly lowered when they are combined with phenoxyethanol. The antimicrobial efficacy of cosmetic preservatives and known allergens of various potency [diazolidinyl urea, methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), methylisothiazolinone (MI) and phenoxyethanol] was tested alone and in various combinations of two or three preservatives together. The preservatives were tested for minimum inhibitory concentration (MIC) values and possible synergy using fractional inhibitory concentration. MCI/MI was the only preservative showing low-level MIC against all four tested microorganisms: Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. Different combinations of the preservatives indicated additive effects against the microorganisms. No combination of preservatives showed any inhibitory action on each other. Challenge tests with different concentrations and combinations were performed in a cosmetic cream. Diazolidinyl urea and MCI/MI alone were ineffective against C. albicans in a challenge test at concentrations up to 16 times higher than the observed MIC values. When combining phenoxyethanol with either one of the allergenic preservatives diazolidinyl urea, MCI/MI or MI, the cosmetic cream was adequately preserved at concentrations well below the preservatives’ MIC values as well as 10-20 times below the maximum permitted concentrations. By using combinations of preservatives, effective preservation can be achieved with lower concentrations of allergenic preservatives.
Int J Cosmet Sci. 2011 Nov 28. Accepted.
In vitro induction of apoptosis, necrosis and genotoxicity by cosmetic preservatives: application of flow cytometry as a complementary analysis by NRU.
de Carvalho CM, de Menezes PF, Letenski GC, de Oliveira Praes CE, Feferman IH, Lorencini M.
Preservatives are used in cosmetics to prevent microbial contamination; however, some preservatives are not free of allergenic and cytotoxic potential. Allergenicity and cytoxicity potentialvaluesare major aspects of preservative safety, which determine limitations and maximum concentration dose in a cosmetic product. The purpose of this study was to investigate and compare the in vitro apoptosis, necrosis and genotoxicity-inducing potential of five different types of preservatives: Phenoxyethanol (PE), Propylparaben (PP), Methylparaben (MP), Benzyl Alcohol (BA), and Ethylhexyl Glycerine (EG). In vitro experiments were carried out on human dermal fibroblasts by a quantitative flow cytometry method, using specific cell markers (Annexin V, Propidium Iodide and H2A.X). We compared the resulting cell viability by means of Neutral Red Uptake (NRU) and established the IC(50) . Our results showed that PE, PP, MP and BA have similar cytotoxic mechanisms (high apoptosis and necrosis levels only at the test concentration of 1%), while EG showed only an apoptosis pathway. For genotoxicity, both parabens yielded the highest values. Results obtained by flow cytometry for necrosis were comparable to those produced by NRU; however, NRU does not distinguish apoptosis from necrosis.