Dry skin, medically termed xerosis, occurs when the skin's outer barrier cannot retain sufficient water or when water is lost from the skin more rapidly than it is replenished. The stratum corneum normally contains water-binding substances and lipids that limit transepidermal water loss. When these components are reduced or disrupted, the surface becomes rough, flaky, tight or cracked. Dry skin is common and can occur temporarily because of environmental conditions or repeated washing, but persistent xerosis can also be associated with inflammatory skin disorders, ageing, systemic disease or medicines. The visible dryness therefore represents impaired hydration and barrier function rather than simply a lack of water on the surface.
Environmental conditions strongly influence skin hydration. Cold, dry outdoor air and indoor heating can reduce ambient humidity and increase water loss from the stratum corneum. Hot showers and baths can remove surface lipids, particularly when combined with soaps or detergents. Frequent handwashing, occupational exposure to water and repeated use of cleaning products can similarly disrupt the barrier. The effect is cumulative: repeated exposure can prevent the skin from restoring its normal lipid organisation between episodes. This is why hands, lower legs and other frequently exposed areas often become particularly dry during cold weather.
Age is an important contributor to xerosis. As people get older, the skin can become thinner and its production of certain lipids and natural moisturising factors can change. Sebaceous gland activity may also decline, reducing the oily component that helps protect the surface. Older adults can additionally have reduced thirst, mobility limitations or environmental exposures that make maintaining comfortable skin more difficult. Dryness associated with ageing is not necessarily a disease, but severe cracking, inflammation or persistent itching can compromise the barrier and increase susceptibility to infection and dermatitis.
Atopic dermatitis and other inflammatory skin diseases can produce severe dryness because barrier function is impaired. In atopic eczema, abnormalities involving proteins and lipids of the epidermal barrier can increase water loss and facilitate penetration of irritants and allergens. The resulting inflammation causes itching, redness and further barrier disruption, creating a self-reinforcing itch-scratch cycle. Psoriasis can also cause scaling and dryness, while contact dermatitis may develop after exposure to irritants or allergens. Dryness is therefore sometimes a manifestation of an underlying inflammatory condition rather than an isolated problem.
Certain systemic diseases can be associated with dry skin. Hypothyroidism can produce dry skin alongside other symptoms of reduced thyroid activity. Diabetes can contribute indirectly through dehydration associated with high blood glucose and through changes affecting skin function. Kidney disease and other chronic illnesses can also be associated with pruritus and dryness. Nutritional deficiencies are less common causes in well-nourished populations but severe deficiencies or malnutrition can affect skin integrity. Persistent, widespread or unexplained dryness accompanied by other systemic symptoms should therefore be evaluated rather than attributed automatically to weather or bathing habits.
Medicines can sometimes cause or worsen dryness. Retinoids, including systemic isotretinoin and some topical retinoids, reduce sebaceous activity or alter epidermal turnover and commonly produce dry skin. Some diuretics can contribute indirectly through fluid balance, while other medicines may have dermatological adverse effects. The exact mechanism depends on the drug. A medicine should not be stopped abruptly simply because dryness occurs; if a new medication coincides with significant skin changes, the prescriber or pharmacist can determine whether it is a plausible contributor and whether an adjustment is appropriate.
Management centres on restoring and protecting the skin barrier. Moisturisers or emollients reduce transepidermal water loss and soften the stratum corneum; ointments are generally more occlusive than creams, while lotions are lighter but may require more frequent application. Applying moisturiser soon after bathing can help retain water in the outer skin. Shorter, lukewarm showers and gentle fragrance-free cleansers can reduce barrier disruption. Persistent inflammation may require treatment prescribed for the underlying condition. Severe cracking, bleeding, infection, widespread rash or persistent unexplained dryness warrants medical evaluation.
Dry skin is therefore usually caused by increased water loss, reduced barrier lipids, environmental exposure, ageing, excessive cleansing or an underlying skin or systemic condition. It can produce scaling, tightness, roughness, cracks and itching, and scratching can further damage the barrier. The most useful distinction is between uncomplicated xerosis and dryness caused by a condition such as eczema, psoriasis, hypothyroidism or medication effects. Protecting the stratum corneum and identifying persistent underlying causes are more effective than simply applying water to the skin, because the central problem is often failure of the barrier to retain moisture.
