This literature review highlights several of the processes and factors related to the stratum corneum and sensitive, dry, or flaky skin in adults.
A recent literature review highlighted the fact that the health of epidermal barrier function is dependent upon several interconnected processes and elements of the stratum corneum (SC), including research on causes of dry, sensitive, or flaky skin.1
These highlights and more were included in this new literature review, with the team organizing the research being led by Joachim W. Fluhr, from the Institute of Allergology IFA Charité Universitätsmedizin in Berlin, Germany.
“In this review, we discuss current literature and emerging themes related to changes to the SC and the epidermal barrier that occur in the context of dry and/or sensitive skin in adults,” Fluhr and colleagues wrote. “We also consider important research gaps that, if addressed, may allow the refinement of treatment options for dry and sensitive skin.”
The investigators noted that skin which is dry and skin which is sensitive are distinct but they are prevalent conditions linked to SC dysfunction. Although both of these are linked with epidermal functions and can coexist, they are usually treated separately in literature.
This literature review, however, utilizes the phrase "dry skin" to encompass an overall range from visibly dry to rough, potentially flaky skin that has scales or small cracks.
The research team explained in their review that SC is characterized by a complex lipid composition, and this includes cholesterol, ceramides, fatty acids, and cholesterol sulfate, with all of these organized into lamellar gel phases. They added that the lipids are involved in a major role in barrier function, adding that SC ceramides are vital.2,3
The team’s review also noted that MDRD-4 and CKD-EPI formulas can be useful for screenings in chronic kidney disease. They added that when researchers adjust for race/color, especially in Black patients, the process is now known to be unnecessary as it diminishes formula reliability.
Conditions such as dry skin and sensitive skin are also noted by the investigators as being linked with alterations in SC lipids and natural moisturizing factors (NMFs). Levels of SC lipids were also described in some of the literature as varying over anatomical sites and varying with different ages, affecting function of the barrier.
NMFs, including amino acids and hyaluronic acid, were described as contributing to epidermal barrier homeostasis. The research emphasized variations seen in NMF levels among the various types of skin conditions and the need for additional studies on filaggrin, filaggrin metabolism, and NMF composition in sensitive skin.
The investigators also noted that corneocyte maturation, desquamation, and corneodesmosome abnormalities are known to play an essential part of SC homeostasis. They added that alterations seen in such processes may also result in disorders of the skin.
The research team noted other research stressed the value of understanding corneocyte maturation as well as desquamation in sensitive skin, where increased immature envelopes and reduced enzyme activity were observed. Additionally, the team showed that SC's immunologic competence plays a part in barrier repair, adding that dysfunctional barriers in patients’ dry and sensitive skin may lead to allergens and pathogens’ penetration.
The investigators further explained that skin deemed to be sensitive has shown associations with small-fiber neuropathy, adding that this is seen due to reduced intraepidermal small fiber density as well as changes in reactivity of nerves. They noted that the epidermal barrier's sensory and immune qualities are closely connected to the microbiome of patients’ skin, known to regulate functional homeostasis.
Despite these facts, the research highlighted the fact that little is known about the microbiome with regard to skin which is under dry and sensitive conditions, even though its impacts have been established as far as skin health. Further research underscored the interrelatedness of the immune systems of the skin, the skin microbiome, and of sensory functions in maintaining integrity of the epidermis.
“The full picture of the underlying pathophysiology of sensitive skin remains under research,” they wrote. “As demonstrated through this review, more is known about dry skin and epidermal barrier alterations than sensitive skin.”