John J. GriWn, Robert F. Corcoran. and Kenn K. kana Hull High School Hull. Massachusetts 02045
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I
The pH of Hair Shampoos A topical high sch001 experiment
During recent yean the topic of p H has been introduced into commercial hair shampoo advertisements. Claims of p H control not only improving the cleansing of hair hut also making hair shinier, bouncier, and stronger are found in these advertisements. Following a discussion and laboratory assignment in measuring p H by different conventional techniques, the topic of p H effects in hair shampoos developed in a Freshman Science class a t Hull High School. The following questions were generated by the students. What pH's would be found in hair shampoos? What effect would the p H factor have on cleansing hair? What p H would be g d for a hair shampoo? In response to these questions the students were invited on an assigned day to bring in different hair shampoos and related toiletries for p H determination. Measurements of the p H of the various shampoos and rinses were then repeated under controlled conditions as part of a Junior class project. Experimental All pH measurementswere made with a Chemtrix, Type 40E,pH meter, using a Broadly James combmation electrodewith the toiletries in a thermostated water bath at 25.5 + 0.5'C. The reproducibility of this pH system was > i0.1 pH units on the non-expanded s d e when used in the pH range of 2.2 to 9.2The meter was calibrated before and during use by standard buffer solutions. Dilutions were made by adding 10 ml of each toiletry ta 90 ml of distilled water. The toiletries reported in this study were purchased between June, 1975 and May, 1976. Results The p H values for the more popular brands of shampoos, both concentrated and dilute, are reported in Table 1. The corresponding measurements for the creme rinses and conditioners are reported in Table 2. Slightly over half of the shampoa tested were on the acid side of the p H scde. The p H range was from 3.3-8.7. All of the creme rinses and conditioners tested were acidic with a p H range of 2.6 to 4.8. Discussion The Relevance of pH in Hair Cleansing
The cleansing power of a shampoo generally refers to the ability of a shampoo to remove grease, dirt, and foreign matter from the hair and scalp ( I ). Grease originates in the hair as sebum, a substance composed primarily of glycerides (50%), waxes (20%),squalene (lo%),and fatty acids (5%)(2). These substances are secreted by the sehacious glands into the hair follicle cell. Sehum moves by capillary action up the shaft of the hair and gives the hair luster and pliability. Oversecretions and accumulated secretions can cause hair to have a greasy appearance. The cleansing power of a shampoo is primarily characterized by the detergent used in the shampoo. A detergent molecule is composed of two functional groups: the polar or hydrophilic group and the nonpolar or hydrophobic group. The function of the polar group is twofold: to attach itself to the hair so as to aid in displacing the grease from the hair and to maintain the detergent's solubility in water (3).The nonpolar group's function is to aid in displacing the grease as well as assisting in the emulsification of the grease. Whether the p H of a shampoo is high or low does not indicate the cleansing power of the shampoo. Hair shampoos
Table 1. p H of Shampoos pH Shampoo
after OH dilution
pH Sham000
after D H dilution
Rite Aid
6.9
Rite Aid Extra Rich
6.9
Johnron & Johnson's Baby Harrison Milk BabY Flex Balram & Protein
6.9
Herbal Essence (dry) Albert0 V O 5
Vaseline lntenS I VCare ~ BabY Bright Side
Z.0
Sunshine Harvest Bonnie Bell ~ ' o r e a Herbal l
Bradleer Tear Free Baby o l d spice Whella Balram Pleil Concentrate Malt Enriched Halo
7.1
Denorex Medi-
7.4
catea Ha~k D.S.T. Treatment
7.5
DO9 Sebulex (pulverized sulfur & ~ a l i ~ ~ l i c acid) Selson Blue Earth Born Green Apple Earth Born Apricot
Clairol Great Body Milk Plus Six (normal) Style Strawberry
Suave Strawberry Essence Suave Lemon Plus Six Herbal Errence (CVS) Clairoi Herbal
Essence Herbal Esrence (delicate hair) Protein 21 (regular) Staff Herbal Essence AVO" Hi.Li9ht (oily hair) Herbal Errence (dry & normal) Landers Castile ojerne Pure Herbal King's Herbal Essence Mild Lemon (Revlon) Con. ditionik Lanolin PIUS Wheat Germ check Mate Dan
6.9 7.0
7.1
7.3 7.3 7.3
7.3
7.3
Tegrin Medicated White Rain Crystal Clear Balsam ~ i a l Herbal White Rain Feberge Organics. Wheat Germ. Oil & Honey Albert0 Balram, (normal) Breck. (norma1 hair) Dial
7.5
Head & Shoulderg control Dandruff ~'Oreal Overnight Balram idry & normal) Lemon U p
7.7
Pharmacy Le mon Scented
8.0
Pet Shoppe. Pet
8.7
Medi-Clean Medicated Pet
8.7
7.5 7.6
7.6
7.6 7.6
7.6 7.7
7.8
7.8 7.8
are adjusted to a p H which among other things is compatihh to the nature of the detergents within the shampoo. A good shampoo should not remove all oils from the hail and scalp. This promotes ideal conditions for scalp diseases. Human skin has a natural acidlayer on its surface witha p H between 3.0 and 5.0. This acid layer is caused by the lactic acid-lactate buffer pair secreted in the eccrine sweat and the fatty acids produced by the sehacious glands. The fatty acids Volume 54, Number 9, .September 1977 / 553
p H of Creme Rinses and Conditioners Creme R i n s e andlor Conditioner
DH
Instant Conditioner Plartlcare,bH Balanced Conditioner Clairol. Long & S i l k y Conditioner Clairol. Long & S i l k y Extra Body Conditioner Albert0 salram Conditioner Harriron emo on c r e m e ninre Earth Born Creme Rinse. Avocado Herbal Errence creme R i n r e & Conditioner Tame Conditioner (dry hair) Tame p H Controlled Creme Rinse
2.6
Wella Balsam
Lemon UD Creme Rinse Breck C r e m e R i n s e
2.7 2.8 2.9
p H after dilution
3.5 3.1 3.3 3.3
2.9 3.0 3.0 3.0
3.5 3.0
3.0 3.2
3.6 3.6
4.3 4.3
4.8
3.1
3.3
4.2
within this layer inhibit the growth of certain bacteria, especially streptococci. In addition, unsaturated fatty acids, especially those having an odd number of carbon atoms, afford a natural protection against fungus infections such as ringworm (4). Undecvlinic acid, for examole, . . is used in "medicated" shampoos: The Relevance of pH in Damaging Hair Hair consists of erouns of amino acids interconnected forming long polype&de'chains. The polypeptide chains are kept in a fixed position relative to parallel polypeptide chains through intermulecular bonding from side chain amino acids. The side chain amino acids constitute approximately 50Ro of the weight of hair keratin (5). The side chain bonding consists of the following types 1)
hydrogen bonding, especially that between adjacent amide and carbonyl groups
2) an acid group from one side chain interactingwitha basic group
on a parallel protein forming a salt bridge 3) cystine disulfide bonds linking adjacent polypeptides (6)
-CHd--S--CHr In water the hydrogen bonds are reversibly broken; this accounts for the ease in manipulating wet hair. In strong acid solutions,pH of 1-2, both the hydrogen bonds and salt links are broken, but the hair is able to maintain its integrity through the disulfide bonding. In the isoelectric region for hair (approximate p H 4-6) the~normalcharge distribution remains unchanged and hair is least swollen and has its maximum wet streneth. At a oHof 12.all three bondsare broken with a suhseqGent dissolution bf hair (7). Commercially available depilatories, such as "Neet" and "Nair" contain strong alkaline ingredients. At 25"C., the p H values for "Neet" and "Nair" are 11.5 and 11.9. resoectivelv. Hobinson ( 8 )has indicated'thai shampoo?iofrelatively low alkslinitv. DH of 8.5. can oroducedamaee to hair cells in the form of &it ends. his is particularly t i e for long hair which bas been subiected to repeated shampoo treatments over a at a typ&al shower &perature of 40°C. A two-year cumulative effect reduces the disulfide bond content to the extent that splitting occurs. Cuticular erosion is readily visible on these ends.
ammonium. sodium. or other available cations. hut can he selectively exchanged by making available (as in certain toiletries) a high concentration of a particular cation, or by the addition of a cation with some surface activity. The addition of polyethylenimines which become positively charged a t a p H of 4 toashampoo of similar p H results in its uptake on hair, especially damaged hair, and reportedly improves compatibility and manageability (10). Other cationic materials can also condition the hair bv reducinr! - electrostatic attraction (11). Laden and Finklestein (12) using dye solutions demonstrated that the rate and extent of sorption of dye in hair could be modified by changing the p H of the system from which sorption occurs. The sorption of collagen derived peptides on peroxide damaged hair has been demonstrated to he an equilibrium phenomenon governed by t h e p H of the peptide solution (13). The pH of Children's Shampoos
Shampoos manufactured for use on infants and children should be formulated to avoid skin and eye irritation as well as eye sting. Eye sting can be minimized by the use of shampoos buffered to a p H close to that found in eve tears. Solutions entering the conjunctival sac with a p H above 7.8 or below 6.6 will oroduce unoleasant sensations. Extended studies have indicated the ;H of lacriminal fluid to be ap~roximatelveaual to that of blood with a D H of 7.4 (14). . . Eye irri6tions can he produced by one or more ingredients within the shampoo. Consumer l ( e ~ u r l schemists found that several commerc~allyavailable haiishampoos caused iris and cornea tissue irritations to rabbits used as test animals (15). Conclusions The DHof shamooos and hair conditioners has been shown to be important n i t only for cleansing hair, but also in terms of im~rovineand enhancine aualities of hair. minimizine irritations to ;he eyes, and stibilizing the ecolo~icalbalance of the scalo. commercial advertisements have effectively stimulated students to exolore bevond the classroom to fmd a relationshio between the concept bf p~ and its use in a practical and adplied sense. Acknowledgment The authors wish to express their appreciation to the followine: Andrew Callahan. and William Willev of Hull Hieh school for their technical assistance; David W. ~annelloof Redkin Laboratories, for suggestions in improving the original manuscript; and the following students a t Hull High School for their enthusiasm in this endeavor: Joel Bloom. Deborah Coash, Sheryl Dobkin, Robert Kraus, Maureen ~ c ~ o w a n , and Vickie Menice. Llterature Cited 11) Bal-, M.S.,andSawn,E.,"Cosmetics:Seienee andTechnolopy," 2nd Ed.,vol. 11, Wilev-Interscience. New York. 1974. o. 75. 12) ~a~s-.. M s..and ~bgarin,E...i~os&iics: Science and ~eehno~agy;2nd ~ d .vol. , I, Wiley-Interacience. New York, 1972. p. 37. 13) Harri, R G., "Principlesand P r a c t i i ifMododCcctifi:6th Ed., Vd. 1,Chemid Publishing Co., Now York, 1973.p. 380. (4) Balsam, M. S., and Sagarin, E.,"Cmmetics:Science and Technology: 2nd Ed., Vol. 111. Wiley-Inferscience, New York, 1974. p. 215. 151 H s m . R. G.. "Prindoleamd Practices of MalornCaemetlrp!'6th Ed..Vnl. 1 Chsmiral , ~ i b i i s h i n b ~N& ~ . . York. 1973, p. 357. 16) H s m , R. G.."Princidesand Prseticesof Modern Caemetim"6th Ed...Val. I..Chemical P"b1khingCo..New York, 1973, p p 351354. (7) H a w , R.G.,"PRnciples and Pmtieesaf McdemCasmetics:6thEd., Vol. 1,Chomical Puhlishine Cn.. New York. 1911. n n 257-111R~
The Relevance of pH for Hair Conditioning Agents
In hair there are approximately 1.5 times as many acidic amino acid side chains available for interaction with basic amino acid side chains from adjacent polypeptides (9).This means that when salt bonds form between an acid carboxvlate group on one polypeptide and a base (ammonium) group on a parallel polypeptide, there will still be a large number of excess acid side chains. These are normally neutralized by 554 1 Journal of ChemicalEducation
11967).
114) Balsam, M. S.. and Sagarin. E., "Cmmetics: Scienee and I, Wiley-Inferscience, New York. 1972. p. 141. 1151 Consumer Reports, 33,529, lo&.1968).
Technology,"2nd Ed.,Vol.
