The pH of Skin

The surface of human skin has a naturally acidic pH in the range from 4-6, probably averaging 4.7. This acidic nature of skin is called the acid mantle and is vital for the proper functioning of skin. The low pH helps to protect the skin from bacterial infection, protects the barrier function of skin and helps the skin enzymes function properly. If the pH varies greatly, skin problems arise which may include infection, dehydration, dermatitis, roughness, acne, irritation, and noticeable flaking.

For a refresher, the pH refers to the concentration of hydrogen ion. It is a logarithmic scale that goes from 1-14 with 7 being neutral, less than 7 acidic and higher than 7 alkaline (basic). The pH of a solution can be measured with a pH meter, pH of skin is more difficult to measure and requires more specialized equipment. Read more here.

 What can affect the skin's pH?

The most common thing that we do that can change the pH of the skin is cleansing the face with soap or other cleansers that have a high pH. Healthy skin can come back to its normal pH after a few hours, but not all skin can tolerate that challenge. Face toners are often used after cleansing to restore the skin pH back to acidic. Toners should always have an acidic pH for that reason. I like to use herbaldistillates/hydrosols for a toner.  Modern face cleansers though are typically not soap and are buffered to be an acidic pH. Soap however has a basic pH of about 10 which cannot be changed, that may work great on most of your body, but if you have problems with skin on the face, do not use soap there. You can find a good face cleanser here that is pH balanced to skin.

People have often asked me about cleaning their face with baking soda. This is a big no no because baking soda has a high pH between 9-10 (similar to soap) and is sure to disrupt the pH balance of skin due to its alkalinity. Even plain tap water can affect skin pH. Theoretically, tap water should be pH 7, but it is typically closer to pH 8 because of impurities.

Age also affects skin pH, increasing as we age. For this reason it is important that products for mature skin have a pH from 4-5. Skin moisture, sweat, sebum, anatomic site, and genetic predisposition also affect skin pH.

The skin's pH is maintained by secretions from the glands of the skin; both eccrine and sebaceous secretions.

Understanding the anatomy and function of skin can help you be a better formulator. If you would like to learn more, download our ebook “The Nature of Skin.”

What is the Best Preservative?

I repeatedly get asked “what is the best preservative to use in my natural product?” so I thought I’d address it here. Basically, there is no ‘best’ preservative and preservatives will behave differently in different formulations. So, unfortunately, there is no way to predict whether or not your preservative will work. It really is a matter of trial and error.

Preserving a product means to inhibit growth of microorganisms. These microorganisms are broken up into two categories; bacteria and fungus (including yeasts). For identification purposes, bacteria are categorized as either gram positive or gram negative. This is dependent on their ability to take up a certain dye which is determined by characteristics of their cell wall. Some preservatives work better at inhibiting one or the other. The term broad spectrum means that the preservative is effective at inhibiting a wide range of microbes in both categories.

Some of the new preservatives, although considered more natural, need to be used at much higher concentrations than some of the ‘tried and true’ preservatives. This may increase the possibility of irritant reactions due to the higher amounts. So please try to use the lowest amount possible that will work in your product.

That said, I’ll go over some of the preservatives that I use for natural products.

Trade Name	INCI Name	usage		Comments
Geogard Ultra (sold by Lotioncrafter as Neodefend)	Sodium Benzoate and Gluconolactone	0.75-2%	Broad spectrum	Approved by ECOCERT. Activity is higher in an acid environment (pH 6).
Sodium Benzoate	Sodium Benzoate	0.1- 1%, lower amounts work fine w low pH	Primarily anti-fungal with less anti-bacterial	Its activity increases in a more acid environment. The most effective pH is around 4, at higher pH levels more sodium benzoate is required.
Biguanide 20	Polyaminopropyl Biguanide	0.2-1.5%	Cationic broad spectrum but sometimes weak on fungus	I like it for clear products like distillates, toners. Do not use with xanthan gum or liquid soap.
Leucidal Liquid	Leuconostoc/Radish Root Ferment Filtrate	2-4%	Broad Spectrum	Approved by ECOCERT. For me this has not worked well in many formulas. I’ve had some luck using it with rather clear toners though.
Potassium Sorbate	Potassium Sorbate	0.1-0.5%	Primarily Anti-fungal	Most active at pH 4-5, use more above that.
Optiphen	Phenoxyethanol (and) Caprylyl Glycol	0.5-1.5	Use between pH 4-8. Broad Spectrum	Has worked well in most products for me
Optiphen ND	Phenoxyethanol (and) Benzoic Acid (and) Dehydroacetic Acid	0.2-1.2%	Works best below pH 6, broad spectrum	Works well in most products
Optiphen Plus	Phenoxyethanol (and) Caprylyl Glycol (and) Sorbic Acid	0.5-1.5%	Works best below pH 6, broad spectrum	Works well in most products
Phenoxyethanol	Phenoxyethanol	0.25-1.0%	Most active against gram negative bacteria	More soluble in oil than water which is why it is often sold in a combination.
Plantaservaitve Wsr (Honeysuckle)	Lonicera Caprifolium Extract, Lonicera Japonica Extract	.25-1%	Broad Spectrum, Must be neutralized with citric acid first.	Has worked well in some situations.
Phytocide OS	Sambucus Nigra Fruit Extract	1-5%	Broad spectrum	This is oil soluble and I’ve found it to work in limited products.
Linatural NLPO	Citrus Aurantium (orange oil), Cymbopogon Citratus (lemon grass oil), Sesamum Indicum (sesame oil)	.75-2.0%	Broad spectrum	Has worked in some products. Has a quite citrusy aroma.

There are other so called natural preservatives besides these including aspen bark, willow bark, and various fermentation filtrates as well as preservatives based on essential oils.

Some products are just harder to preserve than others, particularly those that contain a lot of herbs and nutrients. Bacteria and fungus love herbs and nutrients as much as we do.

I never recommend silver or Tinosan products. I fear that it builds up in the environment and will cause problems with time. Perhaps I’ll be proved wrong but I am just not comfortable using a heavy metal.

There are many other so called natural preservatives that you can learn about initially by browsing supplier’s websites. If you want to try several, you’ll just have to buy a few, use them in your product and see what happens.

Before paying for expensive challenge testing, try challenging them yourself initially. To do this, make your product, split into several jars and use a different preservative in each jar (measuring each carefully). Stick your dirty fingers into the jar daily over several days and let it set for several weeks to see if visible fungus develops. But remember, just because visible fungus doesn’t grow does not mean your product is not contaminated. The word microbe is short for microorganism. These are things that cannot be seen with the naked eye, sometimes they are even too small to see with a standard microscope. But that does not mean they are not dangerous.

Remember that preservatives are necessary to make a safe product. You don’t want your customers rubbing bacteria and fungus on themselves.

Learn more about Sagescript microbiology testing here.http://www.sagescript.com/microbiology

Microbiology & Cosmetics

Many people do not realize that any cosmetic product that is good for your skin is also a good breeding ground for microorganisms; bacteria and fungus. The reason they are called ‘microorganisms’ is because they are so small that they cannot be seen with the naked eye. They are ‘seen’ by growing them on a petri dish filled with nutrient rich agar to promote their growth. One unseen bacterial or fungal cell will reproduce rapidly in the right conditions to form a colony or clump of cells that is seen by the naked eye on the petri dish. Results of microbiology tests are given as colony forming units which represents each cell that reproduced to form that colony.

Excessive amounts of bacteria and fungus can affect the cosmetic in a number of ways; cause odors, destabilize the emulsion, cause color changes. Microorganisms can also affect the consumer negatively in ways ranging from harmless itching of the skin to serious infection; even blindness if the product is used around the eyes.

The most common microbiology tests for cosmetics are the APC and fungal/yeast test. APC stands for aerobic plate count. This involves diluting the cosmetic product and plating a portion of it on an agar plate with specific nutrients that favor bacterial growth. This test will tell you how many bacteria are in the product at the time of testing. The fungal/yeast test is similar but the sample is plated on an agar plate with nutrients specific to favor fungal growth as well as an antibiotic to prevent bacterial growth. This is used because bacteria can grow faster, overgrowing a plate blocking out the fungi growth making it hard to identify. Plates are placed in an incubator and observed at 48 hours for bacterial growth and 7 days for fungal/yeast colonies. Colonies appear as spots on the plates that are small communities of tens of thousands of individual cells that grew from one cell that came from the cosmetic sample.

Interestingly, the FDA does not require any microbiology testing of cosmetics, but it is the responsible thing to do to protect both consumers and products.

Another important test is the Challenge Test or Preservative Efficacy Test. Although expensive ($500 or more) this test is important for products that are widely sold commercially. It will tell you how well your preservative works in your specific formula. For this test, 5 or more known microbes (both bacteria and fungus) are individually added to the cosmetic sample. Plate counts are done at various time points over 28 days or more. The counts in the product should decrease 90% or more over a 14 day period and not increase again after that.

A less effective version of this test can be called the “common usage test”. For this you would first have your product tested to assure it is without significant contamination initially, then use and abuse a sample for 2-3 weeks (sticking fingers into it) knowing that you are introducing bacteria and fungus into it. Then have it tested again to see how your product holds up to that insult. The counts for the second testing should be as low as the first testing. These tests will give information on how well the preservative you use is working in your system.
All cosmetic products containing water or watery substances (aloe, hydrosols, water based extracts, etc) require a preservative to prevent microorganisms from growing. And all such products should be tested to make sure they are relatively free of these microbes. Products that do not contain preservatives will sooner or later begin to grow microbes just as food products will and could become unsafe for the consumer.

New Bacteria Found in Toiletries

If you are a small (or large) producer of skin care or toiletries products here are examples of why it is important to test cosmetic samples for the presence of bacteria and fungus.

Researchers in Japan recently identified a new species of bacteria that was isolated from hairspray. The new bacteria is named Microbacterium hatanonis. This bacteria is related to another bacterium, Microbacterium oxydans previously isolated from hospital material. Scientists do not have enough information to know if this new bacteria species is pathogenic, but similar bacteria have not been found to infect humans. It is however a gram-positive, rod shaped bacterium. The original research was published this month in the International Journal of Systemic and Evolutionary Microbiology.
http://www.sciencedaily.com/releases/2008/03/080307110337.htm

Another more serious case of a contaminated cosmetic product occurred in 2006 in the intensive care unit of a Barcelona hospital. Five patients there developed infections of Burkholderia cepacia that were traced to a moisturizing lotion used in patient care. In this case the infections ranged from bacteremia, lower respiratory tract infection and urinary tract infection. Infections of this type can be life threatening for severely ill patients.
http://www.newsmax.com/health/cosmetics_fatal_ill/2008/01/31/68943.html

It is not common for cosmetics to be contaminated with bacteria or fungus but it does happen. This contamination at times can be a threat to human health as well as damage the product integrity. Microbes can be introduced into a product during manufacturing from the air or equipment that comes in contact with the product, it can be present in one of the ingredients of the product, or it can be introduced into the product by the consumer. Preservatives used in a product should be able to inhibit bacteria or fungus that do occur naturally in a product as well as those introduced by the consumer.

In 1989 the FDA randomly tested department store cosmetics products and found that over 5% were seriously contaminated with a variety of microorganisms. Don’t let your product be one of them. Sagescript Institute offers microbiology testing.