Interdigital erosion refers to the condition where blisters form between the fingers, rupture and ooze, leading to epidermal injury.

Ancient texts record "foot dampness qi (tinea pedis)" and "river snail blisters" as including this condition. For example, Waike Zhengzong states: "River snail blisters often appear on the hands and feet, suddenly as if burned by fire, followed by the appearance of purple, white, and yellow blisters. This is due to the spleen meridian's wind-dampness attacking, which soon enlarges, causing distending pain and discomfort." When this occurs between the fingers, it is referred to as interdigital erosion.

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1. Dampness-heat︰The skin between the fingers becomes flushed, followed by the appearance of blisters ranging from pinpoint to rice grain size, or intensely itchy blisters that rupture when scratched, releasing fluid and leaving bright red, moist, and eroded surfaces with sticky exudate. These symptoms recur intermittently and persist for years without significant systemic manifestations. Patients may experience restlessness and discomfort, and may also have dry stools, dark urine, a red tongue with a yellow greasy coating, and a wiry-slippery pulse. This condition is often caused by dietary irregularities, excessive consumption of greasy or raw foods that generate dampness and stir wind, impairing the spleen and stomach, leading to dysfunction of the spleen in transportation, which manifests as skin erosion. The characteristic skin lesions begin with erythema, followed by small blisters that later erode and exude, with bright red bases, often accompanied by obvious heat signs. Treatment focuses on clearing heat and dispelling dampness, commonly using Clearing Heat and Dispelling Dampness Decoction, or applying purslane herb decoction for soaking, and externally using Licorice Root oil to mix with Dampness-Removing Powder for topical application.
2. Dampness-toxin Invasion︰The skin between the fingers becomes pale or blistered, often occurring at the junction of the finger roots, with a moist and eroded surface, intense itching, and redness after peeling, accompanied by persistent exudation. The exudate is light yellow and relatively clear. After drying, scaling is common, and there are generally no systemic symptoms. The tongue texture is slightly red with a white and greasy coating, and the pulse is slow. This condition is caused by internal dampness accumulation, compounded by working in water or prolonged exposure to water, leading to dampness toxin stagnation in the skin. The characteristic skin lesions include initial whitening or blistering of the skin, followed by peeling, erosion, and continuous exudation, often with scaling after drying. Treatment focuses on eliminating dampness and removing toxins, using the Dampness-Removing and Toxin-Resolving Decoction. For external use, Cangfu Lotion is applied for soaking, followed by a mixture of 30 grams of pine pollen and 10 grams of Realgar Toxin-Removing Powder for topical application.
3. Spleen Deficiency with Dampness Retention︰Deep-seated blisters of varying sizes appear between the fingers, often spreading to the fingers and palms. The blister walls are thick, accompanied by intense itching, and the skin surface usually maintains a normal color. When the blisters rupture, the interdigital areas may become moist and eroded, with profuse thin exudate that often spreads extensively. Upon drying, small dotted scabs may form. Symptoms may also include abdominal distension and fullness, loose stools, a sallow complexion, profuse sweating on the hands and feet, and limb swelling. The tongue coating is white and greasy, and the pulse is slow. This condition is often due to congenital spleen deficiency, leading to impaired transportation and transformation, spleen stagnation by dampness, internal dampness production, stagnation in the skin, and failure to disperse, resulting in steaming and eruption in the skin. The characteristic skin lesions are deep-seated blisters or large blisters that frequently occur between the fingers, on the fingers, or palms, causing unbearable itching. The blister walls are thick, and the skin appears normal. After rupture, the eroded areas may show a pale red complexion or heal with scabbing. Treatment primarily focuses on strengthening the spleen and eliminating dampness, commonly using Dampness-Expelling Stomach Poria Decoction. External treatment is the same as for dampness-heat internal accumulation with erosion.

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1. Waike Qixuan．Ulceration of the hand due to water immersion: "Hardworking people who handle water paddles for long periods without rest may develop wet, ulcerated hands. This is common among professions like lathe workers and dyers. Soaking and washing the hands several times in water can be effective."
2. Waike Dacheng．Eczema on the palmar side of the finger or dorsum of the foot: "It occurs on the hands and feet, resembling the shape of a cornelian cherry, with opposing areas of itching and pain. When it breaks, it oozes yellow fluid that spreads, sometimes healing and sometimes recurring. It is caused by wind-dampness invading the skin and muscles. The primary treatment is to kill worms, using a false hellebore ointment for application."