Most hair and skin care products are composed of ingredients that provide a veritable feast for all types of microorganisms, such as bacteria, fungi, mold and yeast. Water, which is the major ingredient in most shampoos and conditioners, provides a very friendly atmosphere for the growth, propagation, and eventual decay of these microbes.

Once a product becomes contaminated by these types of nasty critters, it becomes — quite literally — a toxic soup. Exposure to a contaminated product can result in both superficial and subcutaneous skin infections and in very rare and extreme cases, systemic infections that can spread to the organs.

The use of various techniques to prevent this type of growth is necessary for the health and well-being of the consumer. Some of the methods used to provide a safe product include the following:

  • • Selecting a pH that is inhospitable to organism growth.
  • • Creating a hostile environment to the organisms.
  • • Adding chemical preservatives.
  • • Using sterile ingredients, processes, and packaging.
  • • Minimizing water content.

Chemical preservatives are added to almost all commercial formulations, due to their ability to provide long-term, broad-spectrum antimicrobial properties at a range of pH’s and temperatures. It is generally necessary to use a combination of two or three different types of preservatives in order to properly protect against the various microbes that can lead to problems. The formulator must also be certain that the preservatives used will not interact with any other ingredients in the product, resulting in either a toxic byproduct or ineffective preservation.

Because the purpose of chemical preservatives is to discourage the growth of microorganisms, it should not be surprising that they are capable of attacking human cells. Preservatives frequently cause dermatological reactions and sensitizations in users of shampoos, cosmetics, and skin care products. Some even have been implicated in more sinister pathologies, such as hormonal problems and cancer. However, in the world of mass-produced products, which are expected to have shelf lives of up to three years, they are necessary. Scientists are continuously working on the development of safer preservatives, so we can expect to see changes in which ones are popular throughout our lifetimes.

There are a large number of preservative types in current use. Formaldehyde donors, such as diazolidinyl, imidazolidinyl urea and DMDM hydantoin, are one group. The parabens are commonly used antimicrobials, as are the isothiazolinones. Cationic surfactants, such as Quaternium-5, have also been shown to inhibit bacterial growth. Aromatic alcohols, such as benzyl alcohol and phenoxyethanol, various mild acids (such as sorbic acid and citric acid), vitamins, and certain essential oils and extracts are also popular. EDTA and other chelators and antioxidants are also part of many preservative combinations found in products.

Formaldehyde donors (diazolidinyl, imidazolidinyl urea, and DMDM hydantoin)

These chemicals are frequently used because they are considered to be effective, providing broad-spectrum protection against bacteria -- particularly Pseudomonas. They are also considered to be safer than formaldehyde itself, because they slowly release only minute amounts of formaldehyde over time. However, dermatologists and allergists do report these to be frequent irritants and allergens in their patients.

A frequently asked question is whether “urea” ingredients are extracted from or somehow related to urine, human or otherwise. The answer to that question is “definitely not.” The word “urea” simply denotes a type of chemical compound that can be found in nature (such as in our metabolic waste), and can also be synthesized in a laboratory.

Parabens: (methyl-, ethyl-, propyl-, and butylparaben): Considered to be very effective biocides against yeasts, molds, and bacteria, this group of preservatives is also popular with formulators due to good thermal flexibility (they can be added to either hot or cold processes) and a tendency not to interact with surfactants in the solution. These are esters of a naturally occurring acid (para-hydroxy benzoic acid, found in blackberries and raspberries). A recently reported study indicated a possible link to the use of parabens and estrogenic-like activity, as well as possible carcinogenic properties. More study will need to be done to prove or disprove any connection between parabens and these health issues, but some people avoid using products containing these chemicals.

Isothiazolinones (methylisothiazolinone and methylchloroisothiazolinone):These chemicals are highly effective against yeasts, molds, and both gram-negative and gram-positive bacteria. However, they are considered to be very strong allergens and irritants of skin and membrane tissue. After a high number of sensitization reports in the 1980s, it was recommended that the isothiazolinones be used in very low concentrations and only in rinse-off products.

Natural preservatives (tea tree oil, grapefruit seed extract, potassium sorbate): These types of preservatives are more acceptable to many users who object to some of the potentially toxic effects of synthetic preservatives. However, many of these either have regular preservatives in them as a result of their processing, or they simply cannot guarantee a healthy, microbe-free product for more than a few weeks or months. This is not necessarily a bad thing, especially for the formulator and purveyor of more “natural” products, but it is important for both the formulator and the end user to understand the limitations of these materials.

Preservatives usually comprise no more than 0.5-2.0% of the total solution by weight, but they can be the source of a lot of concern and confusion to consumers. While they have certain drawbacks, they do manage to help companies provide products free from biological spoilage and with long shelf life, which helps to prevent infections and also provides convenience to the customer. An educated consumer can choose to select products that contain the preservative packages with which they feel most safe from irritation, allergic reaction, or later pathology. If a person wishes to minimize contact with chemical preservatives or avoid them entirely due to concerns about their effects, one must be prepared to keep products in the refrigerator and replace them much more frequently than is currently customary.