Prurigo nodularis is one of the intractable skin diseases whose pathogenesis is not yet fully understood even in modern medicine. However, recent studies are gradually revealing that what the Donguibogam calls disharmony of the zang-fu organs or stagnation of the circulation of qi and blood is closely related, from a modern medical perspective, to complex interactions among the nervous system, immune system, and skin barrier of our body.
The most core symptom, severe pruritus, is not simply a problem of the skin surface, but is directly linked to a hypersensitivity reaction of the cutaneous nerves. Looking at the skin tissue of prurigo nodularis patients, nerve endings called C fibers that transmit pruritus tend to abnormally proliferate and distribute. These nerve endings respond far more sensitively to external stimuli; once pruritus is felt, the brain recognizes it as an intense signal and drives scratching. The act of scratching provides temporary relief, but it re-stimulates cutaneous nerves and induces inflammation, causing greater secretion of pruritus-inducing substances such as histamine. As this process repeats, nerves become even more sensitive, and the skin suffers damage and thickens to form characteristic nodules. It becomes a vicious cycle that feeds on itself.
Abnormalities in the immune system also play a critical role here. Patients with prurigo nodularis often show elevated levels of cytokines such as interleukin-4, interleukin-13, and interleukin-31 associated with type 2 inflammatory responses. These cytokines weaken skin barrier function, activate nerve endings that induce pruritus, and promote skin cell proliferation and fibrosis, contributing to nodule formation. In other words, our body's immune system overreacts to maintain a chronic inflammatory state in the skin, which further exacerbates pruritus and nodules. Diverse factors such as stress, hormonal imbalance, and specific allergens can trigger or amplify this immune response. The wind-heat or damp-heat mentioned in the Donguibogam can be interpreted in modern terms as such an excess state of pro-inflammatory cytokines.
In addition, hypofunction of the skin barrier cannot be overlooked. A healthy skin barrier protects the skin from external stimuli and prevents moisture loss, but patients with prurigo nodularis often suffer from compromised skin barrier function. This makes the skin drier and more sensitive, predisposing it to feel pruritus easily even from minor stimuli, and rendering it vulnerable to the penetration of external allergens and bacteria. Ultimately, a damaged skin barrier deepens pruritus and inflammation, initiating a chain reaction that repeatedly damages the skin.
In conclusion, prurigo nodularis is not a simple skin disease, but a condition that arises and worsens through the intertwined complexity of nervous system hypersensitivity reactions, abnormal immune system inflammatory responses, and skin barrier hypofunction. Therefore, just as the Donguibogam emphasized whole-body balance, modern medicine also considers it crucial to adopt a multifaceted approach that goes beyond simply treating the nodular area to regulate systemic inflammation, stabilize the nervous system, and strengthen the skin barrier.
