Contact dermatitis refers to an inflammation that occurs on the skin or mucous membranes due to an allergic reaction or strong irritation after the body comes into contact with a certain substance. It often manifests acutely, and if exposure is repeated, it can develop into a chronic condition. In Chinese medicine, it is named differently based on the contact substance, such as "chamber-pot dermatitis (contact dermatitis of the buttock)," "lacquer sore," "plaster dermatitis," "acne vulgaris," and so on.

bubble_chart Etiology

Chinese medicine believes that due to innate intolerance, the skin and hair striae and interstices are not dense. Once in contact with certain substances, such as drugs, synthetic fibers, flowers, and plants, it can lead to the invasion of pathogenic toxins into the skin, which stagnates and transforms into heat. The pathogenic heat then interacts with qi and blood, leading to illness. Alternatively, inherent dampness-heat within the body, combined with externally contracted toxic pathogens, can manifest on the skin.

Modern medicine believes that this disease is mainly caused by allergic reactions and direct irritation.

(1) Allergic: Common allergens include chemical fibers, dyes, soap, laundry detergent, alkaline water, topical medications, contraceptive devices and drugs, toilet seats, enema equipment, toilet paper, Chinese Taxillus Herb, feces, and their decomposition products, among other items that may come into contact with the anal area. It occurs through epidermal sensitization, mainly caused by type IV hypersensitivity—delayed allergic reactions. Only a few individuals with specific allergic predispositions develop the disease, and it usually occurs only after the second or multiple exposures. Most allergens are haptens, which, when penetrating the epidermis and binding with epidermal proteins, form complete antigens. Generally, the antigen is phagocytosed and processed by macrophages, then monitored by B and T lymphocytes in the skin. B cells recognize the hapten part, while T cells recognize the protein part. After the skin's first contact with the antigen, it causes blast transformation, with T lymphocytes migrating to local lymph nodes, differentiating into sensitized small lymphocytes, and entering the bloodstream. These sensitized small lymphocytes record information about the antigen's protein part, becoming immune "memory" cells for that antigen part. B cells undergo blast transformation to produce plasma cells, generating humoral antibodies against the hapten part. When the skin contacts the antigen again, such as during the latent period, it continues to produce more sensitized small lymphocytes and circulating antibodies. When there are enough sensitized small lymphocytes and circulating antibodies in the body, re-exposure to the allergen triggers an antigen-antibody reaction, leading to illness, causing epidermal cell injury and dermatitis. At this time, T cells with specific information about the antigen's protein part are stimulated to become "killer" lymphoblasts, while other T cells with intracellular antibodies produce lymphokines. These lymphokines include: ① Mitogenic factor, activating macrophages; ② Migration inhibitory factor, immobilizing the emerged migratory macrophages, turning them into more specific killer macrophages; ③ Chemotactic factor, causing monocytes to migrate into the reaction area and dilating blood vessels; ④ Cytotoxic factor, causing epidermal cell injury at the antigen-antibody reaction site. The antigen-antibody reaction leads to necrosis and damage of epidermal cells in the dermatitis reaction area, causing spongiosis and intraepidermal vesicles. The histamine and other factors released by the antigen-antibody reaction lead to dermal vascular dilation, causing erythema.

bubble_chart Clinical Manifestations

(1) There is a history of contact with allergens or irritants before the onset of the disease. The onset is generally acute, and the skin lesions occur at the contact site.

(2) The severity of the skin lesions is related to the strength of the allergen or irritant, the duration of exposure, the size of the contact area, and the sensitivity of the body. In mild cases, there is only local congestion with clearly defined pale red or bright red patches; in severe cases, papules, blisters, bullae, erosion, and exudation may occur; in cases of strong irritation, skin necrosis or ulcers may result; when the body is highly sensitive, the condition may spread throughout the body. In addition to cutaneous pruritus and pain, a few patients may experience systemic symptoms such as aversion to cold, fever, nausea, and vomiting.

(3) The disease is self-limiting and can heal quickly after the removal of the disease cause. If the disease cause is not removed in time, leading to a prolonged course, it may turn into a chronic condition, resembling eczema-like dermatitis.

(4) In allergic contact dermatitis, the patch test for the contact substance is often positive.

bubble_chart Diagnosis

The diagnosis can be made based on the patient's exposure history, the occurrence of skin lesions at the contact site, typical rash manifestations, and a positive patch test, but it needs to be differentiated from acute perianal eczema.

bubble_chart Treatment Measures

(1) Internal Treatment:

1. Chinese Medicine Treatment: It is advisable to clear heat, cool blood, drain dampness, and remove toxins. Prescriptions that can be selected include: ① Modified Gentian Liver-Draining Decoction, removing Bupleurum and Chinese Angelica, and adding Lalang Grass Rhizome, Dandelion, and Dyers Woad; for headache and fever, add raw Gypsum, Mulberry Leaf, and Wild Chrysanthemum Flower; for severe dampness, add Alisma, Polyporus, and Artemisia Capillaris; for poor appetite, add Dried Tangerine Peel, Atractylodes Rhizome, and Malt; for dry stool, add raw Rhubarb. ② Modified White Tiger Decoction. ③ Ecchymosis Dissipating and Toxin Removing Decoction. After symptoms alleviate, consider taking Gentian Liver-Draining Pill, Qingjie Tablets, Qingre Xiaoyan Tablets, Sanhuang Tablets, etc.

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⑴ Antihistamines: Diphenhydramine 25-50mg or Chlorpheniramine 4-8mg, taken orally 3-4 times daily. Alternatively, Astemizole 10mg, taken once daily, can be combined with Vitamin C 100-200mg taken orally 3-4 times daily.

⑵ Calcium: Oral calcium tablets, intramuscular injection of Vitamin D Colloidal Calcium, or intravenous injection of 10% Calcium Gluconate.

⑶ Adrenocortical Hormones: For extensive and severe skin lesions, Prednisone 10-20mg can be used, taken orally 3-4 times daily. Or Dexamethasone 10-20mg, added to 500ml of 5% glucose solution, intravenous drip, once daily.

⑷ Diuretics: For systemic rash with severe edema, Hydrochlorothiazide 25mg can be taken 2-3 times daily for 2-3 days to help reduce swelling.

(2) External Treatment:

1. For erosive and exudative rashes, 5% Boric Acid Solution, 1% Magnesium Sulfate, 0.1% Alum Solution, or Aluminum Acetate Solution can be used for cold compress. For infections, 1:5000-10000 Potassium Permanganate cold compress can be used.

2. For non-erosive and non-exudative rashes, the above methods can be used, or Calamine Lotion can be applied externally.

3. For chronic eczema-like dermatitis, adrenocortical hormone ointments such as Hydrocortisone Acetate Ointment, Fludrocortisone Acetate Ointment, Dexamethasone Acetate Ointment, Triamcinolone Acetate Ointment, or Fluocinonide Ointment can be used.

4. For redness and papules, Sanhuang Lotion or Calamine Lotion can be applied externally, or Indigo Powder mixed with cold boiled water can be applied 4-5 times daily. For severe swelling, erosion, and exudation, a decoction of Dandelion 60g, Mulberry Leaf, and raw Liquorice Root 15g each can be used for cold compress after cooling. 10% Phellodendron Bark Solution, saline, or 3% Boric Acid Solution can also be used for compress. For erosive and crusted lesions, Indigo Ointment or Qingliang Ointment can be applied 3-4 times daily. For cutaneous pruritus, Foxtail Millet Leaf Lotion or Heizituo Lotion can be used.