Natural skin surface pH is on average below 5, which is beneficial for its resident flora

@article{Lambers2006NaturalSS,
  title={Natural skin surface pH is on average below 5, which is beneficial for its resident flora},
  author={Hans Lambers and Sofie Piessens and Anna Bloem and H Pronk and Peter Finkel},
  journal={International Journal of Cosmetic Science},
  year={2006},
  volume={28}
}
Variable skin pH values are being reported in literature, all in the acidic range but with a broad range from pH 4.0 to 7.0. In a multicentre study (N = 330), we have assessed the skin surface pH of the volar forearm before and after refraining from showering and cosmetic product application for 24 h. The average pH dropped from 5.12 ± 0.56 to 4.93 ± 0.45. On the basis of this pH drop, it is estimated that the ‘natural’ skin surface pH is on average 4.7, i.e. below 5. This is in line with… 
Treatment of Aged Skin with a pH 4 Skin Care Product Normalizes Increased Skin Surface pH and Improves Barrier Function: Results of a Pilot Study
TLDR
Reduction of the increased baseline skin surface pH of the elderly is accompanied by improved epidermal barrier integrity, which normalizes to the physiological pH of 4.5 - 5.0.
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TLDR
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TLDR
The tested pH 5 O/W emulsion seems to improve regeneration and stabilization of pHss, which is a physiologically acidic pH that can be restored by topical formulations.
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The impact of increasing age on body odor has become an important issue as our understanding of underlying skin changes in older people has increased. Therefore, cosmetic skin products especially for
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TLDR
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A Long-Term Study to Evaluate Acidic Skin Care Treatment in Nursing Home Residents: Impact on Epidermal Barrier Function and Microflora in Aged Skin
TLDR
Long-term treatment with pH 4.0 skin care results in a significant improvement in epidermal barrier function compared to identical products with a pH of 6.0, and is recommended to maintain the health of aged skin.
The effect of an acidic cleanser versus soap on the skin pH and micro-flora of adult patients: a non-randomised two group crossover study in an intensive care unit.
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It is demonstrated that the product used in routine skin care significantly affects the skin pH of ICU patients, but not the bacterial colonisation.
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