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Communication • An. Bras. Dermatol. 92 (5) • Sep-Oct 2017 • https://doi.org/10.1590/abd1806-4841.20176049   copy

The pH of the main Brazilian commercial moisturizers and liquid soaps: considerations on the repair of the skin barrier* * Study conducted at the Department of Dermatology and Radiotherapy of the Medical School of Botucatu - Universidade Estadual Paulista "Júlio de Mesquita Filho" (FMB-UNESP) - Botucatu (SP), Brazil.

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract:

The pH of the skin is slightly acidic (4.6 to 5.8) which is important for appropriate antibacterial, antifungal, constitution of barrier function, as well as structuring and maturation of the stratum corneum. This study aimed to evaluate the pH of the main commercial moisturizers and liquid soaps in Brazil. Thus, pH of the products was quantified by pH meter in three measurements. A total of 38 moisturizers and six commercial liquid soaps were evaluated. Mean pH of 63% and 50% of the moisturizing and liquid soaps presented results above 5.5, disfavoring repair, function, and synthesis of dermal barrier.

Keywords:
Dermatitis, atopic; Hydrogen-Ion concentration; Soaps; Wetting agentes

The pH of the skin is slightly acidic (4.6-5.8), which is important for its antimicrobial activity, adequate barrier function, structuring and maturation of the stratum corneum. Age, body topography, skin type, sweat, soaps and other topic agents are variables that interfere with its values.11 Leonardi GR, Gaspar LR, Campos PM. Study of pH variation on the skin using cosmetic formulation s with and without vitamins A, E or ceramide: by a non-invasive method. An Bras Dermatol. 2002;77:563-9.

Atopic dermatitis (AD) is the most studied pathophysiological model of skin barrier defect. In AD, skin pH is commonly higher (7.0-7.5), leading to worsening of xerosis, pruritus and severity of eczema.22 Rippke F, Schreiner V, Doering T, Maibach HI. Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus. Am J Clin Dermatol. 2004;5:217-23.

Acidity of the skin surface is maintained by fatty acids released in sebum, lactic acid and sweat amino acids, as well as products of keratinization and hydrolysis of epidermal peptides, such as filaggrin. All these factors contributing to the reduction of pH are reduced in the stratum corneum of patients with AD.22 Rippke F, Schreiner V, Doering T, Maibach HI. Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus. Am J Clin Dermatol. 2004;5:217-23.,33 Addor FA, Aoki V. Skin barrier in atopic dermatitis. An Bras Dermatol. 2010;85:184-94. Furthermore, skin barrier defect is associated with reduction of ceramides and prophylagrin, with greater transepidermal water loss (TEWL), favoring the penetration of substances that act as triggers for inflammation.33 Addor FA, Aoki V. Skin barrier in atopic dermatitis. An Bras Dermatol. 2010;85:184-94.,44 Lai-Cheong JE, McGrath JA. Advances in understanding the genetic basis of inherited single gene skin barrier disorders: new clues to key genes that may be involved in the pathogenesis of atopic dermatitis. An Bras Dermatol. 2006;81:567-71.

Hydration of the stratum corneum is directly related to damage to the cutaneous barrier and varies according to the body area, due to stratum corneum thickness and to microvasculature. After an injury to stratum corneum, TEWL may increase by more than 10 times.33 Addor FA, Aoki V. Skin barrier in atopic dermatitis. An Bras Dermatol. 2010;85:184-94. Reduction of water leads to cracks in the stratum corneum, allowing permeation of substances of higher molecular weight, including allergens and microorganisms. Even in the absence of eczema, the atopic patient presents skin dryness, with increased TEWL in both lesioned skin and uninvolved skin.33 Addor FA, Aoki V. Skin barrier in atopic dermatitis. An Bras Dermatol. 2010;85:184-94.,55 Seidenari S, Giusti G. Objective assessment of the skin of children affected by atopic dermatitis: a study of pH, capacitance and TEWL in eczematous and clinically uninvolved skin. Acta Derm Venereol. 1995;75:429-33.

Filaggrin is the main peptide responsible for aggregating keratin and other proteins in the upper layers of the epidermis to form the stratum corneum.66 Kezic S, Jakasa I. Filaggrin and Skin Barrier Function. Curr Probl Dermatol. 2016;49:1-7. Its deficiency is common in AD (30%), ichthyosis vulgaris and also in the general population. Filaggrin has its synthesis reduced in alkaline environment, as well as the proteases that cause its degradation have higher activity in media with higher pH.66 Kezic S, Jakasa I. Filaggrin and Skin Barrier Function. Curr Probl Dermatol. 2016;49:1-7.

When pH rises, enzymatic activity leads to an inappropriate desquamation, reducing stratum corneum integrity, in addition to the IL-1β activation, which perpetuates chronic inflammation. Furthermore, production of ceramides is pH-dependent since acid sphingomyelinase and beta-glucocerebrosidase work more actively at pHs between 4.5-5.6.22 Rippke F, Schreiner V, Doering T, Maibach HI. Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus. Am J Clin Dermatol. 2004;5:217-23.

Moisturizers and liquid soaps are two important classes of products used both in the prevention and as coadjuvants of dermatological therapy in AD, and the acidic pH of these products (≤5.5) favors the repair of the cutaneous barrier.22 Rippke F, Schreiner V, Doering T, Maibach HI. Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus. Am J Clin Dermatol. 2004;5:217-23. To date, there are no studies evaluating the pH of the main commercial moisturizers and liquid soaps in Brazil.

A cross-sectional study was performed in which pH of moisturizers and liquid soaps were quantified by the Ultrabasic UB-5 pH meter (Denver Instruments, Denver, USA), from September to December 2015.

The main moisturizers and liquid soaps for dermatological use available in the market (Botucatu-SP, Brazil, in 2016) were selected. After calibration, the measurements were performed in triplicate, by the same operator, directly in the products, and the average of the measurements where considered.

Thirty-eight moisturizers and six liquid soaps were assessed. The pH average of the samples are disclosed in tables 1 and 2. In 24 (63%) moisturizers and three (50%) liquid soaps, pH exceeded 5.5, disfavoring the repair of the cutaneous barrier. In 12 (32%) moisturizers and one (17%) liquid soap, the pH was higher than the physiological skin pH (5,8), disfavoring the antimicrobial function.

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Table 1
Mean pH of the 38 commercial moisturizers tested (alphabetical order)
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Table 2
Mean pH of six commercial liquid soaps tested (alphabetical order)

Indication of moisturizers and soaps in patients with skin barrier defect should consider not only the hydration capacity of the stratum corneum, but also its repair. In addition, it was evidenced the prevention of AD and atopic march in murine model, using acidified moisturizing (pH 2.8).77 Lee HJ, Yoon NY, Lee NR, Jung M, Kim DH, Choi EH. Topical acidic cream prevents the development of atopic dermatitis- and asthma-like lesions in murine model. Exp Dermatol. 2014;23:736-41.

Kubota et al. evaluated 70 patients with AD submitted to rapid baths twice a day at 42ºC in a medium with acidic pH, and observed improvement in cutaneous symptoms in 76% of cases.88 Kubota K, Machida I, Tamura K, Take H, Kurabayashi H, Akiba T, et al. Treatment of refractory cases of atopic dermatitis with acidic hot-spring bathing. Acta Derm Venereol. 1997;77:452-4.

Colonization by S. aureus constitutes an important pathogenic factor in AD due to the production of superantigens and toxins, as well as its capacity to stimulate, expand and maintain the inflammatory reaction. Virulence and multiplication of bacteria reach their maximum at neutral pH, being inhibited in an acidic medium. Potential for adhesion of S. aureus to human keratinocytes also rises with increasing pH.99 Mempel M, Schmidt T, Weidinger S, Schnopp C, Foster T, Ring J, et al. Role of Staphylococcus aureus surface-associated proteins in the attachment to cultured HaCaT keratinocytes in a new adhesion assay. J Invest Dermatol. 1998;111:452-6.

Sasai-Takedatsu et al. assessed 22 patients with AD with no specific treatment; half of them received electrolytic acid water spray twice daily, and the other half received placebo. The treated group presented reduction of AD, improvement of sleep quality and reduction of bacterial colonization.1010 Sasai-Takedatsu M, Kojima T, Yamamoto A, Hattori K, Yoshijima S, Taniuchi S, et al. Reduction of Staphylococcus aureus in atopic skin lesions with acid electrolytic water--a new therapeutic strategy for atopic dermatitis. Allergy. 1997;52:1012-6.

The pH differences identified in this study do not discredit the hydration capacity of the products in the stratum corneum, nor their temporal stability. However, in patients with skin barrier deficiency, as in AD, the pH of topical products should be considered in their indication.

In conclusion, there is an important proportion of commercial moisturizers and liquid soaps with pH above 5.5, which can interfere in function, repair and synthesis of skin barrier.

  • *
    Study conducted at the Department of Dermatology and Radiotherapy of the Medical School of Botucatu - Universidade Estadual Paulista "Júlio de Mesquita Filho" (FMB-UNESP) - Botucatu (SP), Brazil.
  • Financial support: none.

REFERENCES

  • 1
    Leonardi GR, Gaspar LR, Campos PM. Study of pH variation on the skin using cosmetic formulation s with and without vitamins A, E or ceramide: by a non-invasive method. An Bras Dermatol. 2002;77:563-9.
  • 2
    Rippke F, Schreiner V, Doering T, Maibach HI. Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus. Am J Clin Dermatol. 2004;5:217-23.
  • 3
    Addor FA, Aoki V. Skin barrier in atopic dermatitis. An Bras Dermatol. 2010;85:184-94.
  • 4
    Lai-Cheong JE, McGrath JA. Advances in understanding the genetic basis of inherited single gene skin barrier disorders: new clues to key genes that may be involved in the pathogenesis of atopic dermatitis. An Bras Dermatol. 2006;81:567-71.
  • 5
    Seidenari S, Giusti G. Objective assessment of the skin of children affected by atopic dermatitis: a study of pH, capacitance and TEWL in eczematous and clinically uninvolved skin. Acta Derm Venereol. 1995;75:429-33.
  • 6
    Kezic S, Jakasa I. Filaggrin and Skin Barrier Function. Curr Probl Dermatol. 2016;49:1-7.
  • 7
    Lee HJ, Yoon NY, Lee NR, Jung M, Kim DH, Choi EH. Topical acidic cream prevents the development of atopic dermatitis- and asthma-like lesions in murine model. Exp Dermatol. 2014;23:736-41.
  • 8
    Kubota K, Machida I, Tamura K, Take H, Kurabayashi H, Akiba T, et al. Treatment of refractory cases of atopic dermatitis with acidic hot-spring bathing. Acta Derm Venereol. 1997;77:452-4.
  • 9
    Mempel M, Schmidt T, Weidinger S, Schnopp C, Foster T, Ring J, et al. Role of Staphylococcus aureus surface-associated proteins in the attachment to cultured HaCaT keratinocytes in a new adhesion assay. J Invest Dermatol. 1998;111:452-6.
  • 10
    Sasai-Takedatsu M, Kojima T, Yamamoto A, Hattori K, Yoshijima S, Taniuchi S, et al. Reduction of Staphylococcus aureus in atopic skin lesions with acid electrolytic water--a new therapeutic strategy for atopic dermatitis. Allergy. 1997;52:1012-6.

Publication Dates

  • Publication in this collection
    Sep-Oct 2017

History

  • Received
    17 May 2016
  • Accepted
    17 July 2016
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