The pH of Pet & Human Shampoos

BY BARBARA BIRD, CMG

BACKGROUND:  We hear a lot of talk from pet shampoo sales persons that pet groomers should beware of using human shampoos on pets.  One of the reasons given for this warning is that pets and humans have significantly different pH of hair and skin and that products formulated for human pH levels might be harmful to pets. 

             An excerpt from a website giving guidance to pet owners says, “Your dog’s coat and skin is different from your own and requires different grooming products.  The first step is to choose a shampoo that has been formulated for dogs with the right pH and appropriate ingredients for their skin.  Human products are too acidic for your dog’s skin and can strip the natural oils from the coat and skin.” ¹  Recently, this warning has shown up on YouTube as, “The Dangers of Using Human Shampoo on Pets.”  This lecture, sponsored by Petsmart, cites different pH balance as one of the main reasons for concern.  The citing of the differences in pH of pet products as the rationale for admonishment against using off-label products has begun to have the qualities of a myth.  We accept as fact that there is some huge difference between the pH pet and human products.   What is the truth about pH? 

WHAT IS pH?  pH is the measure of the acidity or alkalinity of an aqueous substance.  It measures the single property of producing hydrogen ions in solutions (potential Hydrogen).

The scale ranges from zero to fourteen, with seven being the neutral, the pH of pure water.  pH measurements of less than seven are the acidic range.  The lower the pH, the greater the acidity of the substance.  Above 7 is the alkaline range, with a higher pH being more alkaline.  The pH scale is logarithmic, with each unit of difference on the scale representing a ten-fold change in acidity or alkalinity.  Thus, a solution with a pH of 4.0 is ten times more acidic than a solution with a pH of 5.0, and a solution of 3.0 would be ten times again, or one hundred times more acidic than the solution of 5.0. 

STUDY METHODOLOGY: The author kept a journal, measuring the pH of products from the grooming salon, corporate pet supply stores, drugstores and supermarket, and hair salons.  A total of sixty pet shampoos and forty five human shampoos were tested over a period of a year.  All products were measured with laboratory grade hydrion papers accurate to .5 pH. 

This was the second study initiated by the author on this subject.  In 2001, several members of a groomers’ email group participated the measurement of the pH of over 50 pet and human products.  The results were that the pet products ranged from 2.2-7.5 pH, while the bulk of the human shampoos tested within the 5.0-6.5 pH range.  There was a large overlap of products of both types in the 6.0 pH range.  It appeared that there was more difference among the pet products than between the pet and human products.²

2011 STUDY RESULTS

The list of products tested and pH values is found in Appendix A.

TABLE ONE: Number and Percentages of Pet and Human Shampoos

Along pH Range

pH Range	No. Pet Shampoos	% Pet Shampoos	No. Human Shampoos	% Human Shampoos
<4.5	2	3%	0	-
4.5	0	-	4	9%
5.0	3	5%	6	13%
5.5	4	7%	11	24%
6.0	12	20%	12	27%
6.5	19	32%	7	16%
7.0	11	18%	3	7%
7.5	4	7%	0	-
8.0	4	7%	2	4%
8.5	1	1%	0	-

                      TOTALS             N=60                100%             N=45                  100%

·      The range of pH of the pet shampoos was from under 4.5 through 8.5.  The human products ranged from 4.5 through 8.0.  The pet products showed a slightly broader range of pH than the human counterparts. 

·      The average pH of the pet shampoos was 6.46 and the human shampoo average pH was 5.84, a difference of .62 in average pH.

·      There was an overlapping area in the 6.0-6.5 range. Fifty two percent of the pet products and forty three percent of the human products tested in this range.  Forty eight percent, nearly half, of the total pet & human shampoos tested in the 6.0-6.5 range. 

·      Twenty four percent of the human shampoos tested at 5.5 pH, and thirteen percent tested at 5.0.  Fewer of the pet products tested in this more acidic range, with seven percent at 5.5 and five percent at 5.0.  On the higher end of the scale, more of the pet products tested at 7.0 and above than did the human products.  The human products clustered at the mid-range and lower (more acidic) and the pet products clustered at the mid-range and higher (less acidic, more alkaline).  This grouping is illustrated in Chart Number Two below.

This interesting view is very revealing.  It clearly shows that the human shampoo products are formulated in the more acidic range, as expected.  However, it also shows how few of the pet shampoos are formulated in the range they would be expected to fall – above 6.5.  Forty of the sixty pet shampoos, two-thirds of the sample tested at pH of 6.5 or less, in the acidic range along with 89% of the human shampoos. Pet MD states “Dog shampoos should be in the neutral range, around 7”³.  Only one-third of the pet shampoos tested in the expected range of 7.0 or higher.  Why is this so?

From a formulator’s view.  The cosmetic chemists who are formulating shampoos for pets are often the same persons formulating for human shampoo manufacturers.  They are dealing with the same array of ingredients.  Many considerations come into play around pH.  For example, when Ammonium Lauryl Sulfate is used rather than Sodium Lauryl Sulfate, the solution is formulated at a lower pH to prevent liberation of Ammonia.  Also, when polyquaternium conditioning agents are added, the shampoo needs to be more acidic (typically 4.5-6.0) for the maximum conditioning effect. ⁴ Thickness of a shampoo can also be affected by the pH.  The preservative system used to protect the shampoo from contamination may have pH constraints.  For example, many of the organic acid blends used as alternatives to parabens are effective only at less than 6.0 pH.⁵ The bottom line is that the formulator needs to arrive at a pH where the product will perform well and will be suited to species on which it is used.  It is interesting to notice that as more manufacturers of human shampoo lines enter the pet shampoo arena, the pet products begin to more closely resemble their human counterparts. 

            Notes about the pH of canine skin/hair.  The subject of the pH of canine skin seems to be one of those where “the more we learn, the less we know for sure.”  Although it is true that canine skin has a significantly more alkaline pH than human skin, there is no single agreed upon pH number or specific range.  Studies have been done that measure canine pH from 5.5 all the way to 9.1.  Although some references will state the pH of the dog to be 7.5, they are just citing one study.  One thing is clear, pH of a species exists as a range, and the pH of canine skin seems to be along a rather wide range.  In Skin Diseases of Dogs and Cats, Dr. Steven Melman states that the pH of human skin is 5.2 to 6.2, while dog and cat skin ranges from 6.2 to 7.2 with an average of 6.6

            Small Animal Dermatology, 6^th Edition⁷ notes that, In a dynamic study of skin surface pH in dogs. ((158), the following observations were made: pH values varied at different sites on the skin and varied from day to day; males had significantly higher pH values than females on all sites; spayed females had significantly higher pH values at all sites than intact females; black Labrador retrievers had significantly higher pH values than yellow Labrador retrievers, and Labrador retrievers and miniature schnauzers were significantly different from English springer spaniels and Yorkshire terriers.  Clearly, skin surface pH appears to vary with site, day, coat color, sex, gonadal status, and breed.  In addition, it has been reported that the skin surface pH of an excited dog can increase by greater than 1 unit within 1 minute.⁷

 This is not the only reference to the pH of the dog’s skin varying by breed.  A study by the Royal Canin Research Center found the German Shepherd to have the most alkaline of three breeds tested: the 18 GSD’s tested averaged 8.62 pH. Six Golden Retrievers had an average skin pH of 7.57, and  fifteen Labradors averaged 6.84 pH.⁸   Given that the scale is logarithmic, the German Shepard pH was nearly one hundred times more alkaline than the Labradors.  With all of these variables, it would seem like no one pH point would represent the proper pH for a dog shampoo. 

SUMMARY - MYTHOLOGY OF SHAMPOO pH

            A “myth” is defined as “a widely held but false notion.”

MYTH: Human shampoos are formulated at a much more acidic pH than pet shampoos.  FALSE!  Although some human products might be significantly more acidic than some pet products, more of the pet and human shampoos share the same pH than those that differ. In this study, Forty eight per cent of the total pet and human products shared the pH range of 6.0-6.5.  That’s nearly half of the total sample.  

MYTH: Using a mildly acidic shampoo is harmful to a dog that has a mildly alkaline skin pH.  FALSE!  Recent studies suggest that acidifying the skin of dogs with bacterial and yeast infections promotes healing of those conditions.^9,10  There is no available evidence to support the notion that mildly acidic shampoos damage canine skin. 

MYTH: Using a shampoo with an acidic pH will damage or ruin the “acid mantle “ of the canine skin.  FALSE!   The acid mantle theory proposes that the relative acidity of human skin serves as a protective barrier against infection by cutaneous microorganisms.⁹  The relative alkalinity of canine skin means that dogs don’t have an acid mantle.  Matousek, et al, at the University of Illinois, state that,The relative alkalinity of canine skin may be partly responsible for a higher predisposition to cutaneous infections in the dog compared to other species, such as cats or humans.

MYTH: An acidic shampoo is more harsh and potentially irritating than a shampoo of 6.5 pH or higher.  FALSE!  More acidic is not more harsh.  The harshness of a shampoo has more to do with the character of the cleansing surfactants, the detergency, than with the pH.  A slightly acidic shampoo will leave the hair cuticle tightly closed, resulting in smooth, shiny hair.  Alkaline substances can be more harsh on the hair than acidic products.  A more alkaline shampoo will lift and loosen the hair cuticle and is more suited for shampoos for deep cleansing or color deposit.  This is why it is recommended to use a mildly acidic conditioner following such treatment. 

MYTH: A shampoo will have some long lasting effect on the dog’s skin and hair.  FALSE!  There is no evidence to suggest that a rinse-off shampoo product, or a leave-in conditioner is going to have any prolonged effect on the pH of the dog’s skin.  The natural desire of the body to restore balance will operate.  Matousek, et al found that vinegar spray reduced cutaneous pH to less than 6.0 for an average of 12 hours.  Vinegar is about 2.4 pH, very acidic. 

CONCLUSION: Concerns and warnings about shampoo pH and using a shampoo balanced for the pH of the dog seem to be driven more by business and marketing than by science.  There is no scientific evidence that shampoo having a pH of 5.0-6.0 is harmful to pet skin.  In fact, many pet shampoos share that pH range with human shampoos.  There are, however, good reasons to use a good pet shampoo on dogs: Shampoos formulated for canine hair are designed to clean well and are often geared toward specific jobs or coat types.  Human shampoos are designed for daily or weekly use and may not clean a dirty dog well.  They are also mostly formulated to soften hair, which may not be desirable when scissoring a Bichon or maintaining a terrier coat.  Human hair shampoos are less likely to have ingredients for whitening, promoting deshedding, or serious deodorizing.  Products for the trade allow the groomer to custom pick the right product for a salon-worthy result.  Your professional image is enhanced by your knowledge of product science and your choice of professional pet products. 

REFERENCES

1.     Tips for Dogs with Sensitive Skin, www,petalia.com.au

2.     Bird, Barbara J., Beyond Suds and Scent: Understanding Pet Shampoos and Conditioners,  Birdzeye Press, Tucson, AZ, 2006

3.     Pet MD, Maintaining Your Dog’s Skin pH, petmd.com

4.     Klein, Ken, Shampoo Formulation: The Basics, Cosmetics & Toiletries, May, 2004.

5.     Weber, Klaus, New Alternatives to Paraben-Based Preservative Blends, Cosmetics & Toiletries Magazine, January 2005,Vol.120, No.1, p.57-62.

6.     Melman, Steven A. , Skin Diseases of Dogs & Cats: A Guide for Pet Owners and Professionals, ,Dermapet, Potomac, Maryland, 1994.

7.     Scott, DW, Miller, WH, Griffin, CE, Muller & Kirk’s Small Animal Dermatology, 6^th Ed., 2001, W.B. Saunders (US).

8.     Weber, M, Royal Canin Research Center, 2003.

9.     Matousek, J, Campbell, KL, Kakoma, I, Solter, PF, Schaeffer, DJ, Evaluation of the effect of pH on in vitro growth of Malassezia pachydermatis, Can J Vet Res>v.67(1); Jan 2003. 

10. Matousek JL, Campbell KL, Kakoma I, Schaeffer DJ. The effects of four acidifying sprays, vinegar and water on canine cutaneous pH levels. J Am Anim Hosp Assoc. 39:29-33 (2003)

Originally published in eGroomer Journal, April 2012