180 JOURNAL OF COSMETIC SCIENCE XEROSIS Xerosis or dry skin is characterized by perturbed barrier function, increased transepidermal water loss (TEWL), and retention of adherent squames, which leads to the flaky appearance of cosmetically dry skin. Dry skin is best treated by use of a combination of mild cleansers and moisturizers. Moisturizers typically contain a triad of humectants, emollients, and occlusives (13), and petrolatum is one of the most common and effective occlusive agents (18). PJ forms an occlusive layer on the skin, effectively slowing water loss as measured by TEWL by more than 50%, while certain other oils reduce TEWL by less than 20% (19). Water is instead retained in the skin, thus increasing hydration (20) as evidenced by changes in skin capacitance (21). Petrolatum is the gold standard topical agent for reducing TEWL (22,14). As PJ hydrates the skin, skin suppleness and softness is improved. Unlike other occlusive or vapor-permeable products, petrolatum jelly penetrates the stratum corneum where it diffuses into the intercellular lipid domains (15). Penetration of many other oils is limited to the upper layers of the stratum corneum (23,19). A recent study by Choe et al. (24) also observed increased stratum corneum thickness (32% average) with PJ, it but argues that this may be due to changes in increased absorption of water by corneocytes. Importantly, PJ retards water loss without a decrease in the lipid biosynthetic rate (25,15). This potentially increases its efficacy by facilitating the skin’s own barrier recovery. Many actives have been included into moisturizing creams, claiming to provide superior benefits. However, few studies have demonstrated a superior moisturizing effect over VPJ (26). Cosmetic dry skin may result from environmental factors, such as low humidity and cold temperatures, as well as from intrinsic factors such as age. Skin aging is associated with a degradation in skin barrier function, hence senile xerosis and pruritis are common features in the elderly population (27,28). Routine application of an effective moisturizer, such as PJ or petrolatum-based moisturizers, is critically important in maintaining optimal skin condition. Moreover, epidermal dysfunction and a poor barrier have recently been found to contribute to an increase in age-associated systemic inflammation in mice, while daily rehydration lowered levels of circulating cytokines. Maintenance of a healthy skin barrier may extend well beyond the realm of dermal health alone (29,30). AD AND ECZEMA AD is a common inflammatory skin disease that manifests as dry, scaly, erythematous skin. Dysregulation of the innate and adaptive immune responses contributes to the pathophysiology of AD. However, barrier dysfunction is a key feature of the disease (31). Perhaps the strongest evidence to support this later point is the finding that loss-of-function mutations in the filaggrin gene are a major predisposing factor for developing AD (32). Disruption of the skin barrier integrity allows entry of irritants, microbes, and allergens into the compromised skin, and when set in the context of a dysregulated immune setting, this can lead to the development of allergy and asthma—the so-called “atopic march.” The need for routine moisturization is a well-established part of the skin care regimen for AD suffers (33). Maintenance of an adequate barrier may reduce the need for corticosteroids or calcineurin-inhibitors (34). Studies demonstrate that mild to moderate AD can be improved with a PJ-containing emollient cream (35,36). Norman (37) recommends use

181 Efficacy of Petrolatum of petrolatum under gloves to be worn at bedtime for treatment of eczematous hands. Paraffin-based containing emollients are recommended for the treatment of the severely dry skin found in ichthyosis (38). AD patients experience a higher frequency of skin infections (39,40). Thus, preservation of the barrier is important to protect against further inflammation. Interestingly, patients with AD experience many more skin infections than those afflicted with psoriasis, despite the commonality of a perturbed barrier. It has been suggested that the decreased production of antimicrobial peptides (AMPs) in AD patients may explain the increased susceptibility to skin Infection (41). Surprisingly, PJ has been found to upregulate AMP production in the skin of both healthy patients and patients with AD (17). In the Czarnowicki study, petrolatum, applied under occlusion, significantly increased gene expression of AMPs (including members of the S100 family and cathelicidin) and cytokines (IL1b, Il6, Il8, TNFa), as compared with occlusion alone (17). Increases in AMP protein levels were observed in both subjects with AD and subjects without AD, although upregulation was higher in the subjects without AD. Epidermal differentiation was also assessed in the study. Petrolatum occlusion resulted in an increase in filaggrin and loricrin protein and improvement in the overall differentiation process as assessed by hematoxylin and eosin staining. Finally, decreases in T cell and dendritic cell counts were observed in the AD cohort. The authors hypothesized that the upregulation of the Th17 pathways that underlie the increase in AMP could be mediated by upregulation of the arylhydrocarbon receptor. However, very few polyaromatic hydrocarbons remain in VPJ after purification, and topical hydrocarbons do not penetrate intact or damaged skin (16,10). Overall, the study demonstrates that the benefits of PJ in AD may extend well beyond mere moisturization. BABY SKIN Infant skin (i.e., 3–12 months) has been shown to have different water handling properties versus adult skin, suggesting the barrier properties of infants are not identical to those of adults. Hydration and water content are higher in infants, as measured by Raman spectroscopy and conductance measurements (42). However, in this same study by Nikolovski et al., water-holding capacity was lower, as evidenced by lower levels of natural moisturizing factors and higher TEWL (42). Thus, protecting the delicate and maturing skin of infants is important. PJ is frequently recommended to prevent diaper dermatitis (43,44) and is a favorite for use in pediatric AD (36). Additionally, it is commonly used and recommended by midwives across Africa for skin protection properties before, during, and after birth, as it can be purchased at many local stores at prices typically lower than those of baby lotions (45,46). AD is a common chronic inflammatory skin condition that typically begins in early childhood. Prevalence is at 20% in some countries and is increasing (47). Prophylactic use of daily moisturizers from birth is now widely recognized as a cost-effective means of reducing the risk of developing AD in high-risk infants (48–50). Petrolatum was deemed the most cost-effective preventative strategy when tested on newborns at high risk of developing AD (36). Routine use of moisturizers has been shown to reduce the severity of symptoms in children with mild to moderate AD (51,52). As with adults, the proposed mechanisms for the beneficial effect of emollients in children and infants are focused on barrier repair and decreased TEWL. However, moisturization has also been shown to improve microbial diversity and reduce colonization in patients with AD. In one study, topical treatment with PJ-containing