From the current understanding of the compositional changes in dry skin five aspects of stratum corneum lipid biochemistry need to be corrected:
The lowered levels of ceramides generally.
The phytosphingosine-containing ceramide insufficiency.
The ceramide one linoleate (CEOS) insufficiency.
The lowered covalently bound ceramides.
The precise chain length of the ceramide sphingoid bases and free fatty acids.
Overall, however, the lipid lamellar architecture in the outer layers of the stratum corneum needs to be normalized in dry flaky skin conditions. Evidence also indicates that a reduction in long chain fatty acids also occurs in SLS-induced dry skin. As these lipids are important for inducing an orthorhombic lateral packing state, these will also need to be supplied to the skin to more effectively correct barrier function. Moreover correction of the reduction of SC NMF levels, correction of the aberration of CE maturation, and the impaired corneodesmolysis are needed for dry skin treatments.
Several clinical studies evaluating the effects of ceramides have been conducted recently. However, it is important to remember that to derive the full benefits of ceramide technology formulation into heavy emulsions where other emollients dominant the formulation will be difficult to discern unless the ceramides are at a high enough concentration. Nevertheless, two studies investigating the properties of Locobase Repair cream have found opposite effects on barrier recovery. Barany et al. (108) could not find any improvements to placebo whereas Kucharekova et al. (109) found that the CER NP – containing cream significantly reduced TEWL, erythema, and epidermal proliferation compared with placebo cream. Nevertheless, further improvements in function are observed with complete lipid mixtures. De Paepe et al. (110) have demonstrated improvements in barrier functionality and SC hydration from a lipid mixture of CER NP (0.2%), CER AS (0.1%), and CER UP (0.2%) together with cholesterol (0.25%), linoleic acid (0.25%), and phytosphingosine (0.5%) compared with placebo lotions and a lotion containing only CER NP (0.6%) and CER UP (0.4%). The percentage increases in TEWL and SC hydration are shown in Figure 15. Berardesca et al. (111) have also established that balanced lipid mixtures containing CER NP are effective in improving the barrier properties and clinical condition of skin in subjects with contact dermatitis. Equally convincing are the studies of Chamlin et al. (112) showing that a ceramide dominant barrier repair lipid cream alleviates childhood atopic dermatitis. Over the six-week treatment period TEWL values decreased by 50% and the number of D-squame tape strippings required to break the barrier increased from approximately 12 to 22 strippings, indicating a stronger SC barrier function.
In addition to ceramides, which have been introduced to supplement the SC barrier, (113) phospholipids are also bilayers-forming lipids and when combined with glycerol have been demonstrated to be clinically superior to petroleum jelly in relieving dry skin (114).