Dehydration and dry skin: evidence-based prevention and active ingredients

IN BRIEF

• Dry skin (xerosis) is the result of reduced hydration of the stratum corneum and alterations in barrier lipids.
• Environmental factors (hot water, dry air, UV) and biological factors (aging, genetic variants like FLG) increase the risk of xerosis.
• Some topical active ingredients improve hydration and barrier function: urea, glycerol, ceramides, and hyaluronic acid have different clinical evidence.
• Practical valid choices for the general population include gentle cleansers, moderate water temperature, and regular application of appropriate emollients.
• Available evidence includes experimental studies, observational studies, and some clinical trials; each intervention should be evaluated in the individual context.

Abstract: what does science say?

Dry skin (xerosis) results from a reduction of water within the stratum corneum and/or alterations of the hydrolipidic film that compromise its barrier function. Evidence shows that the loss of barrier lipids (especially ceramides), the reduced presence of natural moisturizing factors, and certain genetic factors (for example, filaggrin gene variants) increase skin vulnerability. Numerous experimental and clinical studies indicate that humectants like urea and glycerol, along with lipid repairers containing ceramides and hyaluronic acid-based formulas, can improve hydration and instrumental parameters (e.g., corneometry, TEWL). However, the quality of evidence varies: many studies are short-term, often industry-sponsored, or conducted on small cohorts. The observed effect depends on the concentration of the active ingredient, the formulation, and the frequency of use, and does not always translate into long-term clinical benefit. To interpret these results, it is necessary to distinguish between associations observed in populations and causal evidence verified by well-conducted randomized trials. Finally, environmental factors (humidity, temperature), personal habits (frequent bathing, aggressive detergents), and systemic conditions (e.g., hypothyroidism) modulate the outcome and must be considered in management.

Why Skin Dries Out: Mechanisms and Triggers

Skin retains water through two main components: the stratum corneum (corneocytes and intercellular lipid matrix) and the superficial hydrolipidic film. When these elements are altered, transepidermal water loss (TEWL) increases, and the skin appears tight, rough, or flaky. Biochemical and physiological literature describes the importance of lipids—particularly ceramides, fatty acids, and cholesterol—in ensuring the cohesion of the intercellular matrix; their alteration reduces barrier integrity. [1] Genetic variants that reduce filaggrin (FLG) production are associated with increased dryness and risk of atopic dermatitis, suggesting a link between barrier component deficiency and skin inflammation. [2] In addition to these intrinsic mechanisms, external factors contribute: prolonged exposure to UV rays, overly hot baths or showers, frequent use of harsh detergents, and low-humidity environments increase water loss and alter the lipid composition of the stratum corneum. [9] Aging leads to a reduction in the production of skin lipids and natural moisturizing compounds, resulting in increased epidermal fragility and decreased recovery capacity after insult. [8] In summary, xerosis is multifactorial: the clinical profile depends on the balance between intrinsic vulnerability and environmental stress load.

At-risk groups and related conditions

Skin dehydration can occur at any age and on any skin type, but there are groups that show greater susceptibility. Children have less active sebaceous glands and a still-maturing barrier, with a higher risk of irritation and redness. The elderly experience structural changes in the epidermis: reduced thickness, lower production of lipids and natural moisturizing factors, and slower barrier repair; these phenomena explain the prevalence of xerosis and itching in the elderly population. [8] Other conditions frequently associated with dry skin include primary skin diseases (atopic dermatitis, psoriasis, ichthyosis) and systemic disorders (hypothyroidism, kidney failure, diabetes) that can alter epidermal physiology and the sensation of dry skin. The mechanisms differ among pathologies: for example, in atopy, alterations in the lipid composition of the stratum corneum are observed, with a reduction in ceramides and variations in the length of fatty acid chains, elements that worsen barrier permeability. [1][7]

Active Ingredients: What the Evidence Shows

Clinical and experimental research has evaluated numerous moisturizing and restorative ingredients. Here, those with the most solid evidence or most frequently studied are presented: urea, glycerol, ceramides, hyaluronic acid, and, emergingly, trehalose. The effects depend on the concentration, formulation (emulsion, gel, cream), and method of use; for many products, the data are more robust for instrumental measurements (e.g., TEWL, corneometry) than for long-term clinical outcomes. [3][5][6][7]

Urea

Urea is a physiological humectant present in the natural moisturizing factor (NMF) of the stratum corneum. Recent reviews have synthesized preclinical and clinical data highlighting its emollient properties, keratolytic effects at high concentrations, and ability to improve gene expression of epidermal differentiation proteins. [3] Clinical studies on 10% formulations show instrumental improvements in hydration and symptom reduction in subjects with senile xerosis or xerosis associated with chronic diseases. [4] The effect is dose-dependent: moderate concentrations (approximately 5–10%) are generally hydrating and well-tolerated, while higher values also exhibit keratolytic activity.

Glycerol

Glycerol is a widely studied humectant polyalcohol: the literature indicates that it penetrates the stratum corneum, helps restore water content, and promotes barrier maturation. [5] Clinical and experimental studies report measurable increases in hydration and improvement in barrier function in the short term. Glycerol is often used in combination with occlusive emollients (e.g., petrolatum) to maximize water retention in the stratum corneum.

Ceramides and Lipid Repair Therapies

Ceramides are key components of the intercellular lipid matrix; quantitative or qualitative deficits are associated with barrier dysfunction, particularly in atopy. Cosmeto-medical therapies that provide lipid mixtures (ceramides:cholesterol:fatty acids in physiological ratios) can improve barrier parameters and reduce symptoms in patients with atopic dermatitis or xerosis; some clinical studies on ceramide-dominant products show improvements comparable to conventional approaches in pediatric and adult settings. [1][7]

Hyaluronic Acid

Hyaluronic acid is a polysaccharide with a high capacity to retain water; topically applied, it can increase corneometry and improve skin appearance. Multicenter studies on specific serums and formulations document significant increases in skin hydration after weeks of use, with good tolerability. [6][12] The effect depends on the molecular weight of HA and the formulation's ability to position it in the appropriate skin compartment.

Trehalose and Other Emerging Humectants

Trehalose is a natural disaccharide studied for its cell stabilization properties under water stress conditions. Experimental data and some cosmetic evaluations show a humectant effect and protection against oxidative stress; however, independent and large-scale clinical evidence is more limited compared to the compounds described above and often comes from industrial tests or small controlled studies. [10]

What this means in practice

For the general public, evidence indicates that intervening in daily routines can reduce the frequency and severity of dry skin. Simple measures, based on clinical and physiological studies, include limiting the duration and temperature of showers, preferring cleansers formulated for sensitive skin, and reapplying emollients to still slightly damp skin to retain water. [9] Choosing a formulation with active ingredients supported by the literature can offer measurable benefits: products containing urea (5–10%) or glycerol show increased short-term hydration, while creams that include ceramides can be useful when an alteration of the lipid matrix is suspected (for example, in atopy) to support barrier function. [3][4][5][7] Topical hyaluronic acid increases the water-binding capacity in the stratum corneum, with demonstrated aesthetic and instrumental effects in multicenter trials. [6] It is important to remember that individual responses vary: skin sensitivity, concomitant clinical conditions, and coexisting pharmacological treatments can influence tolerability and efficacy. In the presence of lesions, infections, or worsening despite self-care measures, a specialist evaluation is recommended.

Limitations of Evidence

Research on dry skin treatment includes studies of various designs: in vitro models, animal studies, observational studies, and controlled clinical trials. Instrumental observations (such as TEWL and corneometry) are useful for measuring physiological changes but do not always reflect long-term subjective experience. Many clinical trials are short-term, with small sample sizes, or industry-sponsored, which can introduce publication bias and limit generalizability. [3][6][7] Furthermore, comparability between studies is often compromised by differences in formulations (active concentration, vehicle), studied populations (elderly patients vs. healthy adults vs. children), and selected outcomes. For example, an improvement in corneometry does not necessarily imply a sustained reduction in the risk of infections or relapses. Distinguishing between observational association and causal proof requires randomized trials, control of confounding factors, and adequate follow-up. In this context, practical recommendations must be cautious and adapted to individual cases.

Key takeaways

• Xerosis is a sign of impaired barrier function; identifying environmental and individual causes is essential.
• Humectants (urea, glycerol) and lipid repairers (ceramides) have evidence to improve hydration and barrier parameters, with differences related to concentration and formulation. [3][4][5][7]
• Topical hyaluronic acid can increase the water-binding capacity in the stratum corneum; effects are related to molecular weight and vehicle. [6]
• Many trials are short-term; independent studies with prolonged follow-up are needed to evaluate lasting clinical effects.
• If dryness is severe, associated with lesions, or does not respond to basic measures, consult a doctor to evaluate systemic causes or specific therapies.

Editorial Conclusion

Dry skin is a common, multifactorial problem that can often be managed with simple interventions and products containing ingredients with proven efficacy. Science offers clear explanations of the mechanisms (alteration of stratum corneum lipids, water loss, reduction of NMF) and supports the use of specific humectants and lipid repairers. However, the variability of formulations and the differing quality of studies necessitate a cautious and personalized approach. The most reliable strategies combine limiting environmental stressors, gentle cleansing, and regular use of appropriate emollients; product selection should consider composition, active ingredient concentration, and individual tolerability. When the condition does not improve or there are associated symptoms, the correct course of action is specialist evaluation.