pH Factor

 pH Factor and  it’s consequences for enhancing Montaser formulation efficacy

Considering the wealth of knowledge available suggesting that the natural skin pH is significantly lower than 5.5, namely around 4.7, It is crucial benefits to formulate skincare products at a lower pH for the following reasons:

Enhanced active penetration

  • the polarity of the acid (e.g., lactic acid) is more compatible with that of the SC than the polarity of the dissociated anion (e.g., lactate) is, which will favor the partitioning of the acid into the SC
  • the permeability coefficients of charged species are, on average, 10,000-fold smaller than of their uncharged equivalents; and
  • the aqueous solubility of an acid is, on average, significantly lower than that of its conjugated anion, which will increase the driving force for diffusion into the SC.

In the case of AHAs, these differences are so extreme that they are all formulated at a low pH. Whether this needs to be done for all acids depends on the dissociation constant (the pKa) of the acid, as well as its aqueous solubility.

b) Inhibited microbial contamination

A lower pH on its own already presents a less favorable environment for bacterial growth. In addition, preservatives such as benzoic acid and sorbic acid, which have not yet received bad press, are more active at a lower pH since their pKas are 4.2 and 4.8, respectively. Similarly, preservative boosters such as 1,2-diols, for example pentylene glycol, 1,2-hexanediol, caprylyl glycol and decylene glycol, among others, are more effective at a lower pH. An example is shown in Figure 7  illustrating o/w-emulsions with 0.6% 1,2-hexandiol (and) 1,2-octanediol at pH 5, 7 and 9 that were each challenged with five usual pathogenic strains.

The best preservation was obtained at the lowest pH, especially for Aspergillus niger, but also for Candida albicans.

 

c) Enhanced chemical stability

Although raw materials will vary, maintaining the chemical stability of the active ingredient could be another reason for formulating around this natural skin surface pH of 4.​A well-known pH- sensitive cosmetic raw material is ascorbic acid (a 3,4-dihydroxy-5H-furan-2-on). It very much prefers a lower pH range, just like dihydrox­yacetone, a tanning agent. Actives with similar sensitive structures include those based on hydroxyphenol derivatives. Therefore, plant extracts containing polyphenols usually also exhibit a better color stability at a lower pH.

Yet another example is phenylethyl resorcinol,b a skin toning agent. This material was incorporated at 0.​5% in aqueous ethanolic solutions, which were buffered at pH 4, 5, 7 and 9, and stored at room temperature. Color measurements were performed on phenylethyl resorcinol measuring the L*a*b* color space before and after 7 and 28 days. The Δb* values (color change relative to t = 0) were used to measure discolor­ation. Figure 8 shows the effect of pH in samples all containing 0.5% phenylethyl resorcinol in 20% ethanol and 0.15% disodium EDTA. Since a lower pH is ultimately better for skin, as has been shown, formulators should not hesitate to formulate at a low pH to benefit from alternative preservation systems or to improve the stability of acid stable actives.

Conclusion

It is surprising that the majority of cosmetic products are still formulated at values of around 6. On one hand, the industry is using active ingredients to help improve the quality of skin, yet on the other hand, sub-optimal cream bases are being used. If the base of a skin care formulation is chosen such that it not only feels right but also does not disturb the natural pH level, effective products can be created.

All Montaser Cosmeceuticals products  are Formulated with a pH of about 4.7 as they are beneficial for the skin because they maintain or even fortify the skin barrier and support the natural skin flora. At the same time, a pH of 4.0 to 5.0 helps reduce the use of preservatives and stabilizes many cosmetic active ingredients.

References

Skin Care Formulary, Cosm & Toilet 117 (7) 72–92 (2002) 

Skin Care Formulary, Cosmet & Toilet 118 (7) 70-101 (2003) 

Skin Care Formulary, Cosmet & Toilet 119 (7) 62–82 (2004)

Skin Care Formulary, Cosmet & Toilet 120 (6) 106–126 (2005)

Skin Care Formulary, Cosmet & Toilet 121 (7) 70–82 (2006)

Skin Care Formulary, Cosmet & Toilet 122 (7) 87–94 (2007)

Skin Care Formulary, Cosmet & Toilet 123 (1) 87–94 (2008)

GM Silva  and PMBG Maia Campos, Influence of a formulation’s pH on cutaneous absorption of ascorbic acid, Cosmet & Toilet 116 (1) 73–75 (2001)