Topical application of lipids to correct abnormalities in the epidermal lipid barrier.

An efficient epidermal barrier is dependent on the production of a stratum corneum (SC) lipid matrix with the correct abundance and composition of different lipid classes – primarily ceramides, cholesterol and free fatty acids. Altered SC lipid production has been implicated in the aetiology of many skin conditions, including atopic dermatitis, psoriasis, dry skin and even skin ageing. Changes in the relative abundance of different lipids, and reductions in the chain length of ceramides and free fatty acids alter the lamellar organization and packing of the SC lipid matrix, leading to impaired barrier function. , Therefore, interventions correcting SC lipid abnormalities have the potential to improve epidermal barrier function and the symptoms associated with a number of skin conditions.

Topical application of lipids has shown potential to restore a healthier SC lipid profile, , and in this issue of the BJD, Danby et al. report the results of a randomized observer‐blinded intrapatient‐controlled study examining the effect of topical lipid application on skin affected by atopic dermatitis. In this study, 34 adults with dry eczema‐prone skin applied a test cream to the forearm and lower leg on one side of their body, and a reference cream to the forearm and lower leg on the other side of their body, twice per day for 28 days. The test cream contained ceramides, triglycerides and cholesterol, as well as humectants. Following treatment, participants’ skin was assessed for skin barrier function [transepidermal water loss (TEWL)], integrity (TEWL during sequential tape stripping), cohesion (protein removal during tape stripping), sensitivity (redness and TEWL in response to a sodium lauryl sulfate challenge), hydration (skin capacitance and visual skin dryness) and SC composition and structure [attenuated total‐reflection Fourier transform infrared spectroscopy (ATR‐FTIR)]. The test cream led to significant improvements in all clinical measures compared with the reference cream, and exploratory ATR‐FTIR revealed changes in lipid content and packing in SC treated with the test cream.

The mechanism by which topical lipids improve the SC lipid profile is not fully understood. The lipids contained in the test cream have previously been shown to penetrate the SC, and there is evidence from ex vivo skin that topically applied fatty acids are elongated and directly incorporated into the SC. However, topical lipids may also upregulate keratinocyte lipid synthesis via activation of peroxisome proliferator‐activated receptors. Interestingly, the test cream appeared to have a greater effect size in older individuals, although this was not statistically significant possibly due to the sample size. Intrinsically aged skin in otherwise healthy individuals exhibits changes in SC lipids, with associated decline in skin barrier function. Therefore, although this study focused on volunteers with atopic dermatitis, topical application of lipids may also prove beneficial for healthy older individuals. Indeed, an emollient containing plant oils has been shown to improve skin hydration and barrier function in older individuals.

In conclusion, this study provides further evidence that topical application of lipids can help restore the lipid matrix of the SC, leading to improvement of clinical symptoms. The mechanisms of lipid restoration remain unclear, but this is a promising approach for the treatment of numerous inflammatory skin conditions.