Several epidermal barrier functions, like skin barrier regeneration and antimicrobial response, are related to the acidic nature of the skin surface pH (ss-pH). However, the epidermal acidification is known to be fragile and it is commonly accepted that cosmetic products, especially soaps and skin cleansing products, can induce significant changes in ss-pH. As a consequence, epidermal barrier function and skin microflora are affected negatively. ss-pH even increases after a single washing procedure or after rinsing the skin with water alone. The skin pH recovery needs time up to several hours before it can reach the physiological level. For cosmetic-relevant skin conditions, skin disorders and specific consumer groups, maintaining of the acidic ss-pH is beneficial for epidermal physiology and cutaneous microflora. In this context, cleansing and skin care products with a pH level of 4.0-5.0 may be helpful. In addition, combining the acidic product pH level with the ideal mix of surfactants, thereby enhancing product compatibility and minimizing skin irritation and intolerance, is a major challenge for the future. Beyond innovative cleansing technology, further multifaceted cosmetic research is a prerequisite to get deeper knowledge on the interrelation of product pH level, surfactant composition and corneobiology.

Background: The pH of the stratum corneum (SC) in the elderly is elevated and linked to impaired SC function. Therefore, this paper addresses the question of whether acidic skin care generates positive clinical, biophysical, and microbiological effects in aged skin. Methods: This study was performed to assess skin care effects in nursing home residents (aged 80-97 years). Visual, biophysical, and microbiological methods were used. Subjects were randomly assigned to 1 of 2 groups and treated over 7 weeks with skin care products adjusted to a pH of 4.0 (group A) or a pH of 6.0 (group B). Results: Compared to baseline, SC integrity improved significantly in group A (p = 0.007), whereas there was no change in group B (p = 0.672). SC recovery 24 h after perturbation increased significantly in group A (p = 0.004) compared to baseline. The SC recovery in group B was not significant compared to baseline (p = 0.327). Conclusion: 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. In addition, effects on skin dryness and resident flora were demonstrated, but without significant differences, between the 2 groups. Based on these results, we recommend adjustment of skin care products for the elderly to a pH of 4.0 to maintain the health of aged skin.

The physiological skin surface pH is just below 5. With age the skin surface pH increases up to 6. An increased pH correlates with reduced barrier integrity/cohesion. The present pilot study assesses possible normalization of an increased skin surface pH of the elderly and improvement of barrier function via application of ≈pH 4.0 skin care products. Baseline skin surface pH was determined in elderly (80+ years old; n = 15) compared to middle aged adults (31 - 50 years old; n = 15). The effect of o/w emulsions at pH-values of 3.5, 4.0, 4.5 and 5.5 on the skin surface pH was determined in both groups. Further, the effect of a 4-week treatment with a pH 4.0 skin care product on the skin surface pH, skin hydration and barrier integrity was assessed. Thirteen elderly females were involved in this home-in-use test. Increased baseline skin surface pH of the elderly normalizes to the physiological pH of 4.5 - 5.0 over 7 hours after single application of o/w-emulsions with a given pH of 3.5 or 4.0. A 4 week treatment employing the pH 4.0 skin care product improves the epidermal barrier integrity of the elderly significantly (p = 0.005). Reduction of the increased baseline skin surface pH of the elderly is accompanied by improved epidermal barrier integrity. Skin care products for the elderly have to be adjusted in the pH range of 3.5 to 4.0

In summary, topical application of a pH 4.0 product containing plant oils improves epidermal barrier formation and SC lipid ordering and ratio in aged dry skin.

Background Renewed consumer and industry interest in natural ingredients has led to a large growth of natural cosmetics. This has put pressure on formulation skills and product claims when it comes to using natural compounds. Taking a strategic and comprehensive approach in viewing natural ingredients, including natural oils, as ‘active’ ingredients rather than just providing for so‐called ‘natural’ claims, aids both innovation and development. Given the ever‐increasing consumer demand for natural ingredients, and more importantly the demand for effective natural ingredients including plant oils, it is important for the cosmetic industry to re‐evaluate them in this context. Method The objectives of this review are to provide an update of three popular cosmetic plant oils – Sweet Almond, Evening Primrose and Jojoba – in terms of their cosmetic applications as ‘active’ ingredients. This review highlights the activity of these oils, in the management of dry skin, ageing skin, juvenile skin, atopic dermatitis, scalp conditions and their wider potential. Attention is given to formulation considerations where the content of these oils impacts product oxidation, skin penetration and stratum corneum homeostasis. Results Benefits of these oils have been well documented both pre‐clinically and clinically. Historically, they have been used for hundreds if not thousands of years for their management and treatment of various skin and other ailments. Given the discrepancies in some clinical data presented for a variety of dermatoses, the importance of the choice of oil and how to formulate with them within the context of the epidermal barrier function, skin penetration and toxicity cannot be underestimated. Care should be taken in terms of the quality and stability of theses oils, as well as ensuring best formulation type, if the reported activities of these oils are to be achieved with consistency. Despite discrepancies in the literature and questionable study designs, it is clear that Sweet Almond, Evening Primrose and Jojoba oils do have skin care benefits for both adult and juvenile applications. Conclusion They are effective ingredients for skin care preparations to strengthen stratum corneum integrity, recovery and lipid ratio. Nevertheless, further experimental data are required concerning the impact on stratum corneum physiology and structure.