The skin serves as a mirror reflecting the internal health of the body. Winter dry itching, explained through the lung and blood in Korean medicine, corresponds in modern medicine to weakened skin barrier function and the resulting cascade of immune and neurological reactions.
In the epidermis, the outermost layer of the skin, lies a protective barrier called the skin barrier. This barrier consists of keratinocytes layered like bricks and lipids filling the spaces between them like mortar, primarily ceramide, fatty acids, and cholesterol. This skin barrier protects the body from external harmful substances and prevents internal moisture from evaporating outward.
Cold winter winds and low humidity weaken this skin barrier. In a dry environment, the lipids between skin cells are easily damaged or depleted, creating microscopic gaps in the barrier. Internal moisture evaporates rapidly through these gaps, leaving the skin parched. This is referred to as transepidermal water loss. As transepidermal water loss increases, the skin loses elasticity and becomes rough. Showering with hot water or using alkaline soaps frequently also contributes to breaking down this barrier.
When the skin barrier is damaged, external harmful substances such as allergens, bacteria, and viruses penetrate into the skin more easily. The immune system detects these invaders and initiates an inflammatory response to defend itself. During this process, substances such as pro-inflammatory cytokines are released, causing redness and pruritus. This marks the onset of asteatotic eczema or dermatitis.
Furthermore, ongoing dryness and inflammation make sensory nerves in the skin hypersensitive. Specialized nerve endings that detect itch, known as C fibers, are distributed across the skin surface. In dry, inflamed skin, these nerve endings become abnormally active, triggering itch sensations even from minimal stimulation. Specific receptors like TRPV1 can also be activated, leading to itching accompanied by warmth and pain. This leads into the itch-scratch cycle, where scratching inflicts further damage on the skin barrier and intensifies inflammation.
Winter dry itching is therefore not simply a matter of dry skin, but an interplay of skin barrier damage, immune responses, and neurological hypersensitivity. Just as Korean medicine views this as an imbalance within the body, modern medicine identifies the disruption of the skin's microenvironment and physiological function as the core issue. Relieving this discomfort requires restoring the inherent health of the barrier rather than merely suppressing the itch.
