Talk to many health-conscious consumers today about shaving products and one of their main topics of concern is the use of allegedly dangerous ingredients in the formulation of many brands. Sodium lauryl sulfate and parabens both fall in this category. Are these ingredients really dangerous or have they received a bad rap? Or does the answer lay somewhere between these two extremes?
Sodium dodecyl sulfate (SDS; also known as sodium lauryl sulfate, or SLS): Is a synthetic detergent obtained by treating lauryl alcohol with sulfur trioxide or other sulfur compounds. SDS is a coarse powder that is often used as a foaming agent or detergent in soaps. Commercial SDS is often a mixture of other alkyl sulfates, dodecyl sulfate being the main component. The structure of SDS is somewhat similar to that of sodium laurate, which is the salt of a natural fatty acid obtained by saponification of fats and a component of most sops and shaving creams. The hydrocarbon tail of both SDS and sodium laurate is, in fact, identical. A sulfate group replaces the carboxylic acid group in SDS, this replacement makes SDS a more powerful detergent than sodium laurate. Sulfonate cleaners like SDS do not form insoluble precipitates in hard water and for this reason, they have become a popular choice for cosmetics, household cleaning and personal care products. SDS can be found in a variety of products including, laundry detergents, liquid soap, all-purpose degreasers, shampoos, and toothpaste. In medicine, sodium lauryl sulfate is used as a laxative in enemas, and as an excipient in some dissolvable caplets. SDS can also be found in candy.
What does SDS do?
Like all detergents, SDS removes oils from the skin and can cause eye and skin irritation, and due to its versatility at dissolving oils, it has a wide variety of industrial applications: the same properties that make SDS useful for cleaning your hair make it also useful for cleaning your clothes or a garage floor. Obviously, different applications demand changes in concentrations or strength and that explains the versatility of SDS. In addition, these same properties make SDS a potentially effective topical microbicide that can also inhibit, and possibly prevent, infection by various viruses.
How bad can SDS be on your skin?
SDS has been shown to irritate facial skin after prolonged and constant exposure (more than an hour) in young adults. SDS may worsen preexisting skin conditions in individuals with chronic skin hypersensitivity. According to a report published in the Journal of The American College of Toxicology in 1983, concentrations as low as 0.5% could cause irritation and concentrations of 10-30% caused skin corrosion and severe irritation. The report concludes that “Tests show permanent eye damage in young animals from skin contact in non-eye areas. Studies indicated sodium lauryl sulfate kept young eyes from developing properly by possibly denaturing the proteins and not allowing for proper structural formation. This damage was permanent.”
Is SDS carcinogenic?
SDS is not carcinogenic when either applied directly to skin or ingested. In fact, no interaction between SDS and DNA has been found in vitro or in vivo. SDS is not listed as a carcinogen by either the Occupational Safety and Health Administration (OSHA), the International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP). Despite some evidence to the contrary, including a podcast from the American Cancer Society indicating that no link between SDS and cancer has been found, this urban legend remains and continues to be widespread in many circles. A panel of scientists of the Cosmetic Ingredient Review (CIR) stated that both SDS and ALS (ammonium lauryl sulfate) “appear to be safe in formulations designed for discontinuous, brief use followed by thorough rinsing from the surface of the skin.” The idea that SDS is carcinogenic likely started in the 1970s when some shampoos where found to be contaminated with nitrosamines, which are carcinogenic. Instead, the ethanolamine lauryl sulfates used in these shampoos were found to be responsible. Since, the nitrosamine contamination has been removed.
Parabens are a family of small organic compounds derived from para-hydroxybenzoic acid that are obtained industrially by esterification. Para-hydroxybenzoic acid is a natural compound synthesized by all plants. Among the members of the family methyl and propyl parabens are the most common but definitely not the only ones with industrial applications. The structure of parabens is somewhat similar to benzoic acid and its derivatives. Both parabens and benzoates can be used to inhibit microbial growth. Parabens are found in nature in berry grains like barley, onions, carrots and peaches. Parabens can also be found as food additives in cheese, vinegar, soft drinks and beer. Parabens are used frequently in many pharmaceutical and cosmetic applications because of their low cost. Although all industrial parabens are synthetic, their structure in some cases is identical to those found in nature.
What do parabens do?
Parabens are efficacious at inhibiting micriobial growth and for this reason parabens are commonly used as preservatives in many pharmaceutical and cosmetic formulas, extending the shelf life of products. Parabens are known to have low toxicity and there is no evidence of accumulation after ingestion or direct application on the skin. These acute test show only mild irritation when applied to the skin. Methyl paraben and Propyl paraben are stable, non-volatile compounds and have been safely used as antimicrobial preservatives in foods and cosmetics for over 50 years. When administered chronically, parabens show “no observed negative effects” (NOEL) at concentration up to 4000 mg/kg. The European Cosmetic Toiletry and Perfumery Association COLIPA regarded these experiments as ‘irrelevant’ as “Parabens are hydrolyzed in the skin and we have data to show that none are entering the blood stream”, and dismissed further experiments to address the claims. Parabens are also known to have local anesthetic effect.
How bad are parabens for the skin?
At the concentrations used to preserve cosmetics and medicines, parabens may sensitize and cause topical contact dermatitis. It is believed that persons sensitive to parabens may develop dermatitis from parabens in food and medicines. A study also found when applied on the skin, methyl paraben can react with medium wave ultraviolet radiation and increase DNA damage and skin aging.
Are parabens carcinogenic?
To date, no causal link between parabens and cancer exists. However, small amounts of parabens in the order of 20 nanograms per gram have been found in breast cancer tumors and this has led some investigators to believe that the presence of parabens may be correlated to incidence of breast cancer. In addition, a study correlated age of breast cancer diagnosis to the use of deodorants and underarm shaving. This led the main author of the article to propose the existence of a link between underarm hygiene and breast cancer. The conclusions derived from these studies have propelled a wave of concerns about the safety of parabens in cosmetics and their potential implication in cancer. Since many plants produce parabens, it is not clear that those found in tumors came specifically from topical application of cosmetics. Para-hydoxybenzoic acid, a common component of urine is a product of hydrolysis of parabens. The presence of this compound is attributed to breakdown (deamination) of the amino acid tyrosine that has very similar chemical structure. Para-hydroxybenzoic acid is believed to be essential for synthesis of ubiquinones (coenzyme-Q) a key compound in respiration. An observation that seems puzzling perhaps inconsistent with the results of the studies of parabens is that parabens and not para-hydroxybenzoic acid are the chemical species found in breast tumors. The other piece of data to consider is the ability of parabens to mimic estrogen, a hormone with clear role in tumorigenesis of breast cancer. The ability of parabens to mimic estrogen is considerably lower than other hormones and can only be measured when applied in concentrations 25,000 times higher than those required for parabens to be effective as preservatives. Furthermore, the ability of parabens to mimic estrogen in vivo is much lower than what was found in in vitro experiments.
The bottom line is that although all the research points towards both SDS and parabens being safe for use in cosmetics, there are still aspects of their effect that have not been addressed or completely elucidated. Although only a minority of people have stopped eating mangoes or blueberries because they contain parabens or stopped using dishwasher soap because it contains SDS, there is a growing trend of preferring more “natural” shaving products, even though this designation is completely arbitrary. For instance, naturally occurring chemicals, like arsenates, strychnine and diphtheria toxin epitomize groups of natural compounds that are not necessarily safe or good for humans. The good news is that both SDS and parabens can be substituted for other ingredients without loss of performance. If you decide to use product containing these chemicals, the goal, as always, lies on minimizing exposure. Exposure to chemicals can be compared to photography, where exposure depends on two factors concentration and exposure time. If the toxicity of a chemical is high, small concentrations are sufficient to cause toxic effects. On the other hand, compounds considered safe can cause death if ingested in large quantities in short periods of time, water is the quintessential example of this category.
As consumers, we should push for legislation leading to more stringent research protocols that would determine the effects of these and other chemicals that technology has placed in our path but we should also be mindful of the integrity of the research professionals dedicated to carry out the studies. Although a lot can still be done to guarantee the safety of cosmetics and other products, subscription to conspiracy theories or other urban legends on the subject that are often driven by ignorance and pursue a definite agenda, usually commercial, to discredit a particular industrial sector and propel another, should be avoided. The best approach is to address safety questions with unbiased education but this requires a specific background in a scientific field and this is not easy or practical to obtain. Uneducated customers are easy prey of unscrupulous campaigns.