Concern
Dry skin (xerosis) is skin whose barrier loses water faster than it can replenish it, leaving tightness, flaking and roughness. Low humidity, harsh cleansers, hot water and aging are common drivers. Humectants such as hyaluronic acid draw water in, ceramides replenish the barrier and occlusives seal it. Apply moisturizer to slightly damp skin within three minutes of bathing.
Dryness is a barrier dysfunction in which skin loses water faster than it can retain or replenish it, presenting as flaking, tightness, dullness, and roughness. Mild dryness reflects routine over-cleansing or environmental exposure; chronic dryness signals a deeper deficit in skin lipids (ceramides, cholesterol, fatty acids) and humectant content (the natural moisturising factor). Effective treatment hydrates and replenishes the barrier through three layered actions: humectants that draw water in, occlusives that seal it in, and barrier actives that rebuild the lipid mortar. The BIOSAR Hydraderm range delivers this layered hydration and visibly plumps dehydrated skin.
Epidemiology
Dry skin (xerosis) is among the most common dermatological complaints across age groups and climates. Population studies estimate that roughly 50% of adults in temperate climates experience symptomatic dryness during winter months, and 20–25% of adults in arid regions report year-round xerosis (Source: Hashizume, J Dermatol 2004). Prevalence rises sharply after age 40: the natural decline in stratum-corneum lipid synthesis, sebum production, and natural moisturising factor concentration drives objective xerosis in approximately 75% of adults over 75. Climatic factors compound the picture: low ambient humidity, central heating, harsh winters, and frequent hand-washing each increase transepidermal water loss. In hot, dry climates, intense sun exposure, low humidity, and pollutant-driven barrier disruption make routine ceramide-rich moisturisation a year-round clinical priority rather than a seasonal one.
Why it happens
Dry indoor heating, arid outdoor climates, and air-conditioned workspaces reduce ambient humidity below the 30% threshold at which transepidermal water loss accelerates sharply. Cold winter air holds less moisture than warm air, and forced-air heating compounds the deficit indoors. Layered humectant plus occlusive routines and indoor humidifiers each measurably reduce winter xerosis.
Sulphate-based cleansers, hot water, and twice-daily aggressive washing strip the lipid barrier and elevate stratum-corneum pH. The damage compounds: each wash reduces ceramide content, and lower ceramide content means each subsequent wash penetrates deeper. The corrective is structural: pH-balanced sulphate-free cleansers, lukewarm water, and once-daily cleansing for most adults.
Sebum production falls roughly 50% between ages 20 and 60, and stratum-corneum lipid synthesis declines in parallel. Natural moisturising factor concentration drops with reduced filaggrin turnover. The combined deficit produces the characteristic xerosis of skin over 60: fine scaling, tightness, and reduced elasticity that respond to layered humectant plus ceramide replacement therapy.
Atopic dermatitis (eczema), psoriasis, ichthyosis, and contact dermatitis each present with significant barrier dysfunction and chronic dryness. Filaggrin loss-of-function mutations affect roughly 10% of European populations and predispose carriers to lifelong xerosis even without overt eczema. Ceramide-rich emollients and prescription anti-inflammatories share management of these phenotypes.
Isotretinoin produces near-universal xerosis and cheilitis at prescribed doses through reduced sebaceous output. Diuretics, oral retinoids, certain chemotherapy agents, and some psychiatric medications similarly impact skin hydration. Adjunctive ceramide-rich moisturiser and lip balm reduce discomfort and improve adherence to the underlying regimen.
Water above 40°C strips lipids from the stratum corneum within minutes, and prolonged immersion actually dehydrates skin by leaching water-soluble NMF components. The clinical guidance is counterintuitive but well-evidenced: shorter, cooler showers preserve barrier function; moisturiser applied to slightly damp skin within three minutes of bathing locks in the hydration that remains.
Mechanism
Skin hydration is the product of three biological systems working in concert. When all three perform well, the surface is supple, smooth, and reflective. When any one of them fails, the visible signs of dryness emerge. Understanding the system that has slipped clarifies which moisturiser ingredients earn space in the routine, and why the same product can transform one person's skin and barely affect another's.
The body holds approximately 60% of its water by mass. The stratum corneum is the gatekeeper that decides how much of that water diffuses out into the air. Healthy skin maintains TEWL at roughly 5–10 grams per square metre per hour. Dry, compromised skin commonly measures 15–30 g/m²/h, sometimes higher. The water that exits is not replaced as fast as it leaves, and the stratum corneum dehydrates below the 10% water content threshold required for normal enzymatic desquamation.
When stratum-corneum hydration drops below this threshold, corneocytes fail to detach individually and instead shed in visible clumps: the flaking, scaling, and roughness that define clinical dryness. The intervention is structural: occlusive ingredients reduce TEWL by 30–50% within hours of application. Petrolatum remains the most studied occlusive (cuts TEWL by ~99% over twelve hours); dimethicone, squalane, and shea butter offer lighter alternatives. Layering occlusive over humectant is the biophysical reason a moisturiser applied to damp skin outperforms the same product applied to dry skin.
The mortar between corneocytes is a precisely structured lipid mix: 50% ceramides, 25% cholesterol, and 15% free fatty acids by mass. This ratio is not arbitrary: it forms a lamellar bilayer that water cannot easily traverse. When any component drops, the bilayer reorganises into a less ordered structure, and the barrier loses its water-retention capacity. Ceramide synthesis falls with age, with frequent exposure to surfactants, and in inflammatory dermatoses such as eczema and atopic dermatitis.
Topical replacement is the targeted intervention. Ceramide NP, ceramide AP, and ceramide EOP (the three most abundant endogenous forms) incorporate into the lipid bilayer when applied at physiological concentrations. The ratio matters: published studies show that 3:1:1 cholesterol-to-ceramide-to-fatty-acid mixtures restore barrier function in two to four weeks, whereas individual ceramide application alone is significantly slower. BIOSAR formulations follow this stoichiometry, supplemented with squalane and phytosterols to mimic the full sebaceous lipid profile that aging skin no longer produces in sufficient quantity.
Inside each corneocyte sits a pool of small, water-binding molecules collectively called the natural moisturising factor: free amino acids, pyrrolidone carboxylic acid (PCA), urea, lactate, and various salts. NMF accounts for roughly 20–30% of corneocyte dry weight in healthy skin and is the molecular reason skin holds water osmotically against a drying environment. NMF is generated by enzymatic breakdown of filaggrin during keratinocyte differentiation, and its concentration falls when differentiation is disturbed by inflammation, age, or genetic filaggrin loss-of-function variants (common in atopic dermatitis populations).
Topical humectants supplement the depleted NMF pool. Glycerin at 5–20% concentration draws water from the dermis and atmosphere into the stratum corneum and is the single most studied humectant in dermatology. Hyaluronic acid binds up to 1,000 times its weight in water; low-molecular-weight fragments penetrate the upper stratum corneum while high-molecular-weight forms remain on the surface as a hydrating film. Sodium PCA, urea (at 5–10%), and panthenol each contribute. The clinical pattern is reliable: humectant-only routines in low-humidity environments can paradoxically worsen dryness. The humectant pulls water from the dermis upward when there is no atmospheric moisture to draw from. This is why an occlusive layer applied over a humectant in dry climates is non-negotiable, and why the BIOSAR Hydraderm sequence layers humectant essence under ceramide cream rather than relying on either alone.
Pharmacist's note
If patients adjust only one habit, we ask them to apply moisturiser to slightly damp skin within three minutes of bathing — never to fully dry skin. The water already on the surface is the water you are trying to seal in. This single change measurably lowers transepidermal water loss and outperforms switching to a more expensive moisturiser applied at the wrong moment.
From the BIOSAR ranges
Each formula is built around actives at effective concentrations, manufactured to GMP and ISO 22716 standards.
Hydraderm60 ml
Shea Butter · Urea · Soy Protein
Hydraderm60 ml
Zinc Oxide · Almond Oil · Olive Oil
Hydraderm60 ml
Tea Tree Oil · Shea Butter · Panthenol
PureLove150 ml
Aloe Vera · Glycerin · Coconut Oil
PureLove100 ml
Almond Oil · Coconut Oil · Sunflower Oil
PureLove50 ml
Hyaluronic Acid · Shea Butter · Jojoba Oil
PureLove50 ml
Zinc Oxide · Shea Butter · Panthenol
Nutriva100 ml
Avocado Oil · Almond Oil · Argan Oil
Hydraderm200 ml
Shea Butter · Glycerin · Oat Extract
Serenvit30 ml
Peptides · Vitamin E · Collagen
Hydraderm60 ml
Urea · Salicylic Acid · Shea Butter
Hydraderm200 ml
Almond Oil · Shea Butter · Glycerin
Hydraderm50 ml
Hyaluronic Acid · Ceramide · Shea Butter
Hydraderm200 ml
Hyaluronic Acid · Aloe Vera · Glycerin
Serenvit30 ml
Hyaluronic Acid · Panthenol · Aloe Vera
Sunprotex50 ml
Zinc Oxide · Hyaluronic Acid · Colloidal Oatmeal
Key actives
Lightweight carrier oil. Fast-absorbing nourishment suitable for daily body use.
Botanical humectant used as a comforting base across serums, baby care, and cleansers. High concentrations deliver noticeable cooling and hydration.
Its fatty acids reinforce the lipid layer to reduce moisture loss and leave skin and hair softer.
Plant oil rich in oleic fatty acids, vitamin E and phytosterols. It sinks into dry, depleted skin to replenish softness and lasting comfort, leaving body and hands nourished with a supple, non-greasy finish.
It forms an emollient, occlusive film that softens, shields and gives structure to the formula.
Its cationic structure helps maintain formulation stability and a clean, fresh surface feel without altering the product texture.
Botanical with soothing properties, traditionally used on reactive skin. Delivered as oil and extract for complementary comfort and barrier support.
Skin-identical lipid. Rebuilds the barrier between corneocytes and restores comfort to dry, dehydrated skin.
It coats and softens the surface with an occlusive film that helps reduce moisture loss.
The science
Dryness is a barrier deficit: skin loses water faster than its lipids and humectants can hold it. Hydraderm answers on three fronts together — Hyaluronic Acid pulls water in, Ceramides rebuild the barrier, and Shea Butter with Squalane seal it, delivering hydration that lasts.
Related conditions
If you have sensitive skin, you have probably been told it is in your head — by a product that says "gentle" on the label, by a friend whose skin tolerates everything yours cannot, sometimes by a professional who could not find a visible cause for the symptoms. It is not in your head. The mechanisms are measurable, the biology is mapped, and the care that follows from understanding them is what the Sensimed range was built around.
The first time you notice it is rarely a wrinkle. It is a quality of light — the way your skin catches it differently in a morning mirror, or the photo where you look more tired than you feel. The mechanism is real (collagen synthesis slows; elastin fragments; barrier turnover lengthens), but the felt experience comes first. Serenity Age is the range BIOSAR built for that pivot — Retinol for visible renewal and collagen support, peptides selected for documented signaling activity, and the SPF discipline that protects every other active you apply.
Tightness usually signals barrier impairment — either insufficient lipid content or over-cleansing. Switch to a gentler cleanser and add a lipid-rich moisturizer containing Ceramides or Squalane. Improvement typically appears within one week.
Water intake matters for general health but does not directly hydrate the skin surface. Topical humectants, occlusives, and emollients are what keep water where the skin needs it.
Dry skin tolerates less exfoliation than oily skin. Once or twice a week with a gentle acid (Lactic Acid or PHA) is sufficient. Over-exfoliation worsens dryness.
Dry skin lacks oil (a skin type). Dehydrated skin lacks water (a temporary state). Both need hydration, but dryness also requires lipid replenishment — Ceramides, fatty acids, and plant butters.
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