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Year : 1990  |  Volume : 56  |  Issue : 6  |  Page : 434-437

Comparative measurement of irritant properties of toilet bar soaps on human skin

Correspondence Address:
Sanjay Singh

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Source of Support: None, Conflict of Interest: None

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Ten commonly used toilet bar soaps were tested for their respective irritancies usin Kligman.and Wooding's technique of . 9 evaluation of mild irritants of human skin. Five per cent soap soulations were prepared and their pH measured, IT 50 and irritancy scores were calculated. There was to correlation between pH and IT 50 or irritancy scores and lux pink was least irritant followed by New Cinthol, Pears and lifebuoy.

Keywords: Toilet bar soaps, pH, irritant properties.

How to cite this article:
Singh S, Singh G, Pandey S S. Comparative measurement of irritant properties of toilet bar soaps on human skin. Indian J Dermatol Venereol Leprol 1990;56:434-7

How to cite this URL:
Singh S, Singh G, Pandey S S. Comparative measurement of irritant properties of toilet bar soaps on human skin. Indian J Dermatol Venereol Leprol [serial online] 1990 [cited 2020 Aug 13];56:434-7. Available from:

Soaps and cosmetic material have been recognized as a potential source of cutaneous irritation[1]. We have to consider this aspect when a patient with an eczematous condition asks as to which soap he should use. Also, though cosmetic ingredients are usually irritant only in a small percentage of population, the importance of ensuring low irritancy is obvious since countless units are sold. With the low reaction rates in mind, the actual usage which may be the only wholly dependable method for such testing, is impractical to the extreme, since staggering number of subjects will be required. Kligman and Wooding's technique of testing mild irritants of human skin[2] was used in this study since it is a form of bioassay which involves intensification of effects.

  Materials and Methods Top

We selected 10 commonly used soaps [Table - 1] after consulting shopkeepers both from the rural and the urban areas of Varanasi. 5% solutions in distilled water were prepared. The pH of these solutions were determined using century CP 901 digital pH meter.

Upper back of ten normal human volunteers was chosen as the test site. 0.5 cm2 patches of lint were cut. 0.5 ml of soap solution was sufficient to load a patch completely, it was applied to the lint pieces with a tuberculin syringe. Patches were covered with polythene paper of 1.0 cm2 size. These patches were kept in place by applying cotton backed adhesive tapes.

The patches were removed everyday and the application sites were examined after fifteen minutes in bright day light. On the site showing unmistakable erythema, no further patch was applied. At other places patches with respective solutions were applied at exactly the same site. This was repeated till erythema, the end point, appeared.

Kligman[2] has defined IT50 as the estimated number of days of continuous exposure, which produces a threshold reaction in 50% population.

This method of calculation of IT - 50 is as follows

1) From day-to-day observation of the subjects, a table is prepared showing the number of subjects having irritation on day 1 to day 10 of the observation period [Table - 2]

2) A separate graphs is drawn for each soap on the log probability paper taking 6% of subjects having 'irritation' on the vertical axis against the 'elapsed time in days' on the horizontal axis. The best straight line is drawn through the plotted points [Figure - 1] showing the graph for Rexona soap)

3) On this line, the value of days corresponding to 50% of subjects having irritation is noted. This value is IT - 50 of the soap

Another simpler, but somewhat less precise method of knowing the irritancies was devised by us. Since the subjects were observed for a maximum of 10 days, 10 points can be given to the soap which showed erythema on the first day, 9 to the one showing erythema on the second day and so on. The total of values for each soap was called the irritancy score'.

  Results Top

Our detailed observation of the number of subjects having irritation corresponding to the elapsed time in days is shown in [Table - 2]. IT-50 of all the soaps studied is shown in [Figure - 2]. [Table - 3] shows the pH of 5% solution, IT 50 and irritancy scores of different soaps. Thus the results obtained by both methods of calculation are more or less the same. IT 50 ranged from 5.5 for Lux Pink to 2.0 for Rexona. Irritancy score ranged from 48 to 75.

  Comments Top

The procedure of calculating IT50 attains its best precision when concentration is such that the individual reactions are scattered throughout the test period, with both a zero and a 100% reaction point. This was achieved in this study. It is to be noted that the end points in this technique are 'all or none' choices i.e. they are quantal responses. No attempt to grade the reaction was made, thus eliminating the element of observer's variation. Another handicap with scoring systems is that the reactions to different irritants may be qualitatively quite dissimilar. All or none reactions depend upon a single quality, erythema, which is a common denominator of all irritant reactions.

It is to be stressed that irritant capacity is always relative, never absolute. Thus, we can say that a particular soap is either more or less or equal in irritancy as compared to the other.

The subjects include in the study were Indians; 9 were males and one was female, their ages ranged from 24 to 40 years and the study was conducted in the months of July and August 1987. These specifications make the results more meaningful, but they remain valid for other conditions since they are comparative measures of irritancies.

The irritant properties of soaps do not appear to be due to their alkalinity[3]. pH of soaps ranged from 10.11 for New Cinthol to 10.66 for Lux pink. This degree of alkalinity is innocuous for most individuals[4]. This was obvious from this study also which showed no correlation between the pH and IT50. IT50 ranged from 5.5 for Lux pink to 2.0 for Rexona [Figure - 2] and irritancy scores from 48 to 75. The soaps in decreasing order of IT50 (i.e. increasing order of irritant property) were Lux pink, New Cinthol, Pears, Lifebuoy, Human, Margo, Dettol, Palmolive, Crowning glory and Rexona.

A similar study[5] was carried out in 1974 in which one of the present authors (GS) participated

  References Top

1.McCreesh AH and Steinberg M : Skin irritation testing in animals, in : Advances in Modern Toxicology volume 4 Dermatotoxicology and Pharmacology, Editors, Marzulli FN and Maibach HI : Hemisphere Publishing corporation, Washington, 1977; p 193-210.  Back to cited text no. 1    
2.Kligman AM and Wooding WM : A method for the measurement and evaluation of irritants of human skin, J Invest Dermatol, 1967; 49 : 78-94.  Back to cited text no. 2    
3.Bettley FR and Donogue E, Brit J Dermatol, 1969; 72 : 67. quoted in, Griffiths WAD, Ive FA and Wilkinson JD : Topical therapy, in : Textbook of Dermatology, Fourth edition, Editors, Rook A, Wilkinson DS, Ebling FJG et al : Blackwell Scientific Publications, Oxford, 1986;; p 2529-2573.  Back to cited text no. 3    
4.Blank IH : The mechanism of action of soaps and detergents on the skin, In : The evaluation of therapeutic agents and cosmetics. Editor, Sternberg TH : Mc Graw-Hill Book Company, New York, 1964. quoted in 5.  Back to cited text no. 4    
5.Singh R and Singh G : Evaluation of irritant properties of different toilet bar soaps, Ind J Dermatol Venereal Leprol, 1975; 41 : 99-102.  Back to cited text no. 5    


[Figure - 1], [Figure - 2]


[Table - 1], [Table - 2], [Table - 3]


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