In previous work,1 the authors explored the benefits of Fischer-Tropsch (FT) synthetic waxes for petroleum jelly production. Petroleum jelly is widely used in personal care and is mainly prepared from blends of paraffin wax, microcrystalline wax and mineral oil. Paraffin wax is obtained by purifying slack waxes, but due to changing worldwide demand, their availability is expected to decrease. This presented the need to identify alternative wax sources to produce petroleum jelly, and the authors found that FT waxes provide advantages including improved sustainability and availability, as well as low aromatic and sulfur-based components.
As an extension of their previous work, here the authors assess the performance of cream and petroleum jelly formulas containing different amounts of FT wax, to determine whether its moisturizing effects compare with traditional mineral-derived products. From this, additional future research will be carried out.
Skin and Moisturization
To understand moisturization, it is first important to consider some biology. Biological skin aging occurs beginning at the age of 25 in a natural physiological process,2 although factors such as exposure to sunlight (UV), cold and air pollution may accelerate this process. In addition, the modern diet, which often contains high levels of refined foods, stress, sleep deprivation and lack of exercise contribute to premature skin aging.3 Skin is one of the most complex human organs. With a total area of approximately 2 m2, it is the largest organ of the human body and has roughly 4 million sensory receptors.4
As the external boundary of the body, the skin provides protection and regulates both body temperature and sensory perception. Healthy skin has a natural defense system consisting of: secretions from sebaceous and sweat glands, the skin’s own moisturizing factors, amino acids and lactic acid.3 This so-called protective acid mantle covers the surface of the skin like an invisible, extremely thin film. A good skin care routine will help protect the body—and reduce aging—by cleansing moderately so as to avoid depleting the horny cells, skin lipids (required for skin protection) and water; as well as moisturizing. Skin cleaning products should range between pH 5–6 so as not to disturb this protective, thin acid film.5
Besides these protective elements, epidermal water content is crucial for skin plasticity and the prevention of dry skin.6 Water originates in the deeper epidermal layers and moves upward to hydrate cells in the stratum corneum (SC), eventually evaporating. The SC architecture is the most important factor in water flux and retention in the skin, and in overall levels of moisturization.7 When there is low moisture in the SC, enzymes do not work efficiently and corneocytes accumulate on the skin surface, producing signs of dry skin.
Moisturizing treatments involve repairing the skin barrier, retaining and increasing water content, and reducing transepidermal water loss (TEWL). These treatments also restore the ability of the lipid barrier to attract, hold and redistribute water, and assist in maintaining skin integrity and appearance. Cosmetic products perform these functions by acting as humectants, emollients and occlusive agents.8 Emollients are mainly lipids and oils that hydrate and improve the appearance of skin by contributing to softness, flexibility and smoothness via effects related to skin barrier permeability and repair.9 The spreadability or lubricity of moisturizers contributes to consumer satisfaction and product preference.10 Consumers desire smooth skin following moisturizer application, and emollients fill the cracks between clusters of corneocytes. Emollients are usually not occlusive unless they are heavily applied.
Humectants enhance water absorption from the dermis into the epidermis and in humid conditions, they also help the SC to absorb water from the external environment. Humectants may also have emollient properties.11, 12 Occlusives, in contrast, reduce TEWL by creating a hydrophobic barrier over the skin and contributing to the matrix between corneocytes. However, they are limited by their odor, potential for allergy and a greasy feel.13
Petroleum jelly is one example of a lipid-based occlusive ointment that is insoluble in water. It also qualifies as an emollient, which means it can soothe and moisturize the skin. Petroleum jelly is one of the most cost-effective moisturizing agents,13 softening skin and protecting against wind burn and chapping in cold and wind. Despite its impressive moisturizing properties, many consumers refrain from applying it to their faces for fear of clogged pores. However, petroleum jelly was found to be, and is classified as, noncomedogenic.14
Moisturizers also act to reduce skin friction and increase hydration by providing water directly to the skin from their water phase and by increasing occlusion, as measured by a decrease in TEWL.9 Generally, ideal moisturizers should13 hydrate the SC, reducing and preventing TEWL; make skin smooth and supple; aid in restoring the lipid barrier, i.e., duplicating and enhancing skin’s natural moisture retention mechanisms; absorb rapidly to provide immediate hydration; and provide long-lasting effects, all while maintaining cosmetic elegance and consumer acceptance. The present study evaluated such parameters via corneometer measurements, visual assessments and TEWL measurements.
Materials and Methods
To evaluate the effects of FT waxes in skin, cream and petroleum jelly products were tested for moisturizing efficiency in blind clinical trials conducted at the Medical University of South Africa, Medunsa Campus, Limpopo. The studies were performed according to good clinical practice guidelines on 25 Caucasian female volunteers by applying products to different sites on their outer calves and measuring changes, as described later.
Skin tests: Methods to evaluate moisture efficiency included corneometera measurements, visual assessments and TEWL measurements. Corneometer assessments were performed prior to product application, one hour after the first application, after the first application with wipe-off, at 48 hr and at 96 hr on clean skin. An expert assessor conducted visual evaluations according to a visual dryness scale one hour after the first application with wipe-off, as well as at 48 hr and 96 hr on clean skin. TEWL tests were performed using a vapometerb prior to product application, one hour after the first application with wipe-off, as well as at 48 hr and 96 hr on clean skin.
The test products included petroleum jellies and creams, as shown in Tables 1 and 2, respectively. Petroleum jellies A, B, C and G were different commercial products, all having raw materials derived from mineral oil. Petroleum jelly E was a predominantly synthetic petroleum jelly containing a 65% FT waxc.
Creams C, D, F and G in Table 2 were formulated (see Formula 1) based on the mineral-derived petroleum jelly products shown in Table 1. Creams B and E contained predominantly synthetic petroleum jellies that contained 65% and 100% FT synthetic wax, respectively; petroleum jelly E was used for cream B. The 100% synthetic petroleum jelly was not included during moisturizing efficiency tests. Cream A was a commercial cream produced by emulsification of low melting FT wax rather than emulsification of petroleum jellies. This formulation contained 20% FT wax.
The average corneometer values at 1 hr, 48 hr and 96 hr of the 25 test subjects are shown in Figure 1 for petroleum jellies and Figure 2 for creams.
Corneometer tests: The differences between the products tested and an untreated site were calculated using a student’s t-test. Statistically significant improvement in skin hydration was measured by the corneometer one hour after applying all A–G petroleum jelly products (p < 0.05). Petroleum jellies B and C were not statistically different (with a confidence interval of 95%) from untreated skin after 48 hr and 96 hr (p > 0.05). Mineral-based products A and G, and 65% FT wax-based product E were statistically different (p < 0.05) from untreated skin in terms of skin hydration levels after 48 hr and 96 hr. Applying petroleum jelly products A, G and E therefore resulted in improved skin hydration 96 hr after application, compared to untreated skin. Statistically significant improvement in skin hydration was measured 1 hr, 48 hr and 96 hr after application of all cream products tested (p < 0.0001). This one-hour reading supports a claim of “locks in moisture” for all products.
Visual grading: Expert grader assessments for the petroleum jelly and cream samples are shown in Figures 3 and 4. Statistically significant improvements in skin hydration were observed at 1 hr, 48 hr and 96 hr after application of all petroleum jelly and cream products (p < 0.0001).
Vapometer tests: Vapometer results are summarized in Figures 5 and 6 for petroleum jellies and creams, respectively. Statistically significant improvements in skin hydration were observed one hour after the application of mineral-based petroleum jelly products A, B and C, and jelly E containing 65% FT wax (p < 0.05). Mineral-based product G was not significantly different from untreated skin, and no statistically significant improvement in skin hydration was observed 48 hr and 96 hr after application of products A–E (p > 0.05).
A statistically significant improvement in skin hydration was observed one hour after applying cream products B, D and G (p < 0.05); note that product B was based predominantly on the synthetic petroleum jelly. Cream A, containing FT wax emulsified cream, showed less of a decrease in TEWL than untreated skin but it was not statistically significant; however, cream A performed better than the other samples at 48 hr and 96 hr. This data point could therefore be due to experimental error and may be ignored; it will be repeated in future evaluations. Only creams A and B exhibited significantly different results (p < 0.05) after 48 hr, compared with the untreated site, and only cream A was significantly different from the untreated site (p < 0.05) after 96 hr.
This article describes the evaluation of cream and petroleum jelly formulas containing FT wax for moisturizing effects in skin. FT wax was shown to perform as well as or better than traditional mineral-derived products. Corneometer values showed FT wax-containing petroleum jellies provided pronounced hydration that was statistically significant, versus untreated sites. Visual assessments for FT wax-containing petroleum jellies and creams showed reduced dryness scores, compared to untreated skin.
Further, TEWL values of jellies showed a significant decrease from that of untreated skin for two mineral based-samples and one predominantly synthetic sample. For creams, TEWL values at one hour were significantly different with one synthetic petroleum jelly-containing sample and two mineral-based samples, compared with untreated skin. TEWL measurements of creams at 48 hr showed statistically significant decreases for two samples based on FT wax, compared with untreated skin. The 96-hour TEWL decrease observed was only significant for one sample based on FT wax.
Thus, based on the described moisturizing efficacy tests, it can be concluded that cosmetic products containing FT synthetic wax perform as well as, if not better than, traditional mineral-derived wax products in terms of improved skin hydration and moisturization. Thus, taken together with previous work, the described FT synthetic wax is a sustainable alternative to paraffin wax that can be successfully used in cosmetic emulsions. It provides unique benefits such as low sulfur and polycyclic aromatic hydrocarbon content. The results shown again confirm the moisturizing efficiency of both traditional and synthetic wax-based petroleum jellies, also when used in cream formulations.
Acknowledgements: The authors would like to acknowledge Sasol Wax (SA) for funding the experimental work described, and Beverley Summers, MD, of the Medical University of South Africa for clinical trial results.
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