Statement 3: Aging-associated changes in epidermal function include a 30% reduction in total lipids in the stratum corneum relative to young skin due to reduced epidermal lipid synthesis.
Ceramides, cholesterol, and free fatty acids are essential constituents of the SC.14,16 They form a highly ordered matrix called the lipid lamellae and fill the space between the corneocytes.14,16 The composition and structure of the lipid lamellae are critically important to the permeability barrier function of the skin and form an effective waterproof barrier.14,16 The composition of SC lipids is influenced by age, genetic disposition, time of year, diet, hormone-mediated sebum production, and medication such as cholesterol-lowering agents.14,16 Reductions in SC lipid content may be due to the delayed barrier recovery in mature skin.6,16 In aged skin, the number and function of sebaceous glands reduce, leading to xerosis.20-23 In mature skin, along with the gradual degeneration of the innervation of the skin and the decrease in the number of sweat glands, the heat balance and cold tolerance of aging individuals deteriorates.20-23
Studies have shown that baseline TEWL rates on several body sites are lower in matured vs young skin.6 The demonstrated TEWL rates on the decollete region correlated positively with age, but TEWL rates on the neck, forearm, and hand were comparable between young and aged women.6
Studies from the mid-nineties have shown that the aged SC displays a >30% reduction in total lipid content compared with young SC due to reduced epidermal lipid synthesis, particularly in cholesterol synthesis, both under basal conditions and after barrier disruption.25,26 Studies have further shown that epidermal dysfunction predisposes to various cutaneous abnormalities, including atopic dermatitis, contact dermatitis, pruritus, and xerosis9,10,20-23,27
In support of evidence that reduced lipid levels contribute to aging-associated dysfunction in the skin barrier, topical applications of SC physiologic lipid mixtures such as ceramides may improve epidermal permeability barrier function.14
Statement 4: In older people, xerosis is significantly associated with pruritus.
Pruritus is common in matured skin and has been attributed partially to a decline in normal physiology due to advanced aging.24,27-31 Pruritus significantly impacts the quality of life and is reported by patients to be as bothering as skin pain or even worse.31 Changes in mature skin structure and its ability to regenerate, along with cumulative effects of the environment, diminish the SC barrier function and hydration.21,24 These changes make the elderly more susceptible to the entry of irritants and allergens through the skin, leading to inflammation and pruritus.24
A cross-sectional study including 756 patients aged 65 and older reported a prevalence of xerosis of 56%.19 Of these patients, 9% had moderate to severe xerosis associated with a significant disease burden, including pruritus and feelings of very dry or unbearably dry skin.19 Another cross-sectional study of a population of 11,730 showed that the prevalence of chronic pruritus was 20.3% in people between 60 and 70 years.30 The large study demonstrated significant xerosis-associated risk factors for pruritus, including older age, female sex, atopic dermatitis, or concomitant treatment that may be associated with xerosis.30 Additional causes of pruritus may include various comorbidities, such as renal failure, cholestasis, systemic infections, diabetes mellitus, liver failure, malignancies, or certain hematological disorders.28-30
Xerosis is often associated with pruritus, mainly involving the extremities, and is more prominent at low temperature and humidity conditions.19,30 The scratching can lead to secondary infections, ulcerations, and chronic wounds.24,27-29
SC lipids containing moisturizers such as ceramides combat xerosis and may reduce pruritus.13 Components of topical products such as polidocanol, menthoxypropanediol (derivate of menthol and an agonist of the TRPM8 receptor), or N-palmitoylethanolamide, a fatty acid, may have antipruritic effects.32-35 A double-blind, vehicle-controlled study including patients with xerosis and pruritus (N=70) showed that those topically treated for 6 weeks with menthoxypropanediol combined with cyclohexane carboxamide reported a significantly more robust and longer-lasting antipruritic effect than those receiving the placebo.34 A study on topically applied N-palmitoylethanolamide demonstrated antipruritic effects in patients with xerosis.35
Treating pruritus with systemic medication is outside the scope of this review and is not discussed here.
Statement 5: Moisturizers containing urea, ceramides, and lactate have shown benefits in promoting a healthy skin barrier structure and function in older people with xerosis.
Skincare using gentle cleansers and moisturizers can promote a healthy skin barrier and is crucial for mature skin to reduce TEWL and minimize exposure to irritants and allergens.14,36-42 Acidification of the SC may improve epidermal structure and function in chronologically aged humans. In aged subjects, using a moisturizer at pH 4.0 for 29 days improved SC hydration and lamellar bilayer structure, along with increased resistance to challenges from topical sodium dodecyl sulfate.36 Following acute SC barrier disruption in aged subjects, a topical pH 4.0 moisturizer improved SC barrier recovery faster while significantly improving SC integrity after 28-day treatments compared with a pH 5.8 moisturizer.37
