Contact dermatitis

Introduction to contact dermatitis Contact dermatitis (contactdermatitis), also known as dermatitisvenenata, is an inflammatory reaction in which the skin or mucous membranes are exposed to certain external stimuli or allergens. The substances causing the disease mainly include animal, plant and chemical substances. Among them, chemical substances are common. Contact dermatitis can usually be divided into two categories according to its pathogenesis: allergic contact dermatitis and irritant contact dermatitis. Other types are: immediate contact, phototoxicity and photoallergic contact dermatitis, systemic contact reactions and non-eczema-like contact reactions. Chinese medicine's paint sore and plaster winds belong to the category of this disease. basic knowledge Sickness ratio: 5% Susceptible people: no special people Mode of infection: non-infectious Complications: skin allergies pruritus

Causes of contact dermatitis

Primary stimulation (25%):

This kind of substance has no individual selectivity, can occur after contact with any person, and has no incubation period. It directly damages the skin through non-immune mechanism. When the irritant is removed, the inflammatory reaction can disappear quickly, such as strong acid and alkali, anyone can contact. At a certain concentration, for a certain period of time, acute dermatitis will occur at the contact site, and the other is a weakly irritating substance such as soap, washing powder, gasoline, motor oil, etc., which is caused by repeated contact for a long time. And the nature and physical state of the primary irritant, individual factors such as skin sweating, sebum, age, gender, genetic background and other environmental factors.

Allergic reaction (25%):

Mainly type IV allergic reaction, is a cell-mediated delayed type hypersensitivity. It does not immediately occur after initial contact with the allergen. After 4 to 20 days (average 7 to 8 days) incubation period, the body is first sensitized and re-contacted. After the allergen, dermatitis occurs around 12 to 48 hours.

Scratch (20%):

Skin lesions are generally limited to the contact area, so that there are many exposed parts, the boundary of the boundary is clear, and the shape is generally consistent with the contact, but the contact can be brought to other parts of the body due to scratching or other reasons, even due to the body. In a highly sensitive state and generalized to the whole body, consciously itching, heavy pain, a small number of patients, especially rashes, can sometimes cause systemic reactions such as chills, fever, nausea, headaches, etc.

Pathogenesis

1. A substance with primary irritation that causes contact dermatitis directly damages the skin through a non-immune mechanism.

2. The process that occurs is generally divided into two phases:

(1) Sensitization stage: a process from initial contact with antigen to lymphocyte recognition and reaction with it. Most allergens are simple molecular substances with low molecular weight (<500-1000), called haptens, only It is immunoreactive and has no immunological activity. When combined with a macromolecular substance in the skin, that is, a carrier protein, it forms a hapten-carrier protein conjugate and becomes a complete antigen. It has immunological activity to stimulate the body to produce an immune response. These carrier proteins are epidermal cells. The membrane protein, most likely an antigen-presenting cell (currently identified as Langhans cells, macrophages, cells in the skin, lymph nodes, thymus, dendritic cells in the spleen, etc.), immunoreactive Ia or HLA -DR, the formed whole antigen is processed by antigen-presenting cells, mainly Langhans cells and macrophages, and the antigen information is presented on the surface of the cell membrane, then moved to the dermis and lymph nodes, and reaches the lymph nodes of the skin lymph nodes. Region, LC carrying antigenic information must present antigenic information to CD4 cells, ie Th cells (T helper cells), which have recognition and binding specificity A specific receptor for amphoteric antigen and MHC class II antigen (Ia/HLA-DR), Th which receives antigen information is activated by IL-1 secreted by LC, cells are enlarged, cytoplasm is abundant, nuclear enlargement, immunity Maternalization, synthesis and secretion of IL-2, while allowing other activated Th to express IL-2 receptor, when Th and IL-2 bind to fully activate, Th begins to proliferate rapidly, producing T effector cells and memory cells The former passes the lymphatic system to the blood circulation and the skin, and the latter persists in the lymph nodes or other organs. It is worth noting that this output function of the lymph nodes plays an important role in the production of contact sensitization. Animal experiments confirm that in contact After 48 hours of dinitroaniline, the lymph node was removed to inhibit sensitization. After 5 days, the resection was not inhibited. The T-effector cells circulated to the whole body to form a systemic sensitization state. The experiment confirmed that the contact sensitization pathway included blood vessels. The access route requires a partial and complete lymphatic drainage, which takes about 5 to 7 days.

(2) Effect stage: also known as the excitation stage or reaction period, and the efferent period.

After the body has been sensitized, if the antigen on the skin persists or the same antigen is re-contacted by the above-mentioned induction, the same process of sensitization, a hapten-carrier protein conjugate is formed, and the Langhans cells of the epidermis pass through the recognition antigen. Processing, processing, presenting antigen information to T effector cells, and reacting with it, T lymphocytes reacting with antigens produce many lymphokines, allowing macrophages to aggregate, activate, and pass LFA1/1CAM1, CD2 /LFA3, ELAM1 and other adhesion factors, continue to attract T-effect cells in the blood circulation, monocytes and neutrophils move to the local, with the participation of cytokines such as IFNr, TNF, sponge formation, monocytes Invasion is characterized by an inflammatory response. This phase only takes 7-8 h and peaks within 18-24 h. Langhans cells play an important role in the process of allergic reactions. It is currently believed that its role as a hapten enters the skin. Hans cells bind and are presented, and the Langhans cells loaded with antigen enter the skin to initiate T cell sensitization. The processing and presentation of antigens is called the induction of cell-mediated immunity. It is still unclear whether the site is in the center, ie lymph nodes or in the periphery, that is, the skin is still controversial. Lymphokines play an important role in the induction and stimulation phases. Lymphokines are produced by lymphoid or non-lymphocytes. In this disease, monocyte chemotactic factor and macrophage migration inhibitory factor play an important role. It is believed that the TH cell is limited by the activation of T cells by the antigen. The contact matter is gas, and the dust can be diffusely occurring. Partial erythema, clear boundary, severe swelling, papules, blisters or bullae on the basis of erythema, erosion, exudation and other damage, if strong acid, strong alkali or other strong chemicals and other primary irritants often Causes necrosis or ulceration, dermatitis occurs in the eyelids, foreskin, scrotum and other loose areas of the skin tissue, the skin edema is abnormally significant.

3. After removing the cause and proper treatment, it usually recovers after several days or more than ten days. However, due to improper scratching or handling, the infection or irritant is not removed in time, causing the disease to become chronic dermatitis, similar to chronic eczema.

Contact dermatitis prevention

1. For substances that are prone to sensitization in daily life, be vigilant when in contact, especially those with allergies, try to stay away from it. If there is a reaction after contact, it should be immediately isolated to avoid continuous contact, and the wound should be timely. Effective treatment to prevent the disease from getting worse. If you have had contact dermatitis, you should try to find the cause of sensitization, remove it, and do not touch it. If it has already occurred, you should immediately treat it properly to avoid scratching, washing or using drugs. Additional stimuli worsen the condition.

2, diet therapy, eat spicy and fried foods, especially in the onset of the disease, usually eat light, avoid eating foods that are allergic, such as wine, seafood, etc., eat more fresh vegetables or fruits.

3, the spirit should be happy, life should be regular, do not overwork.

4, exercise properly, choose some activities that suit you, such as climbing, walking, dancing, etc.

5, according to their physical condition, choose the health food suitable for their own, improve immune function, improve physical fitness, not sick or less sick, improve the quality of life.

Contact dermatitis complications Complications, skin allergies, pruritus

In addition to itching pain, a small number of patients may have systemic symptoms such as aversion to cold, fever, nausea, vomiting, improper scratching or handling, infection or irritants are not removed in time, causing the disease to become chronic dermatitis.

Symptoms of contact dermatitis common symptoms erythematous rash fever accompanied by rash urinary histamine excretion increased acne-like rash exfoliative dermatitis herpes zoster-like appearance ear cavity at the ear swelling of the mass of light sensitive skin damage

symptom

According to the course of the disease, it is divided into acute, subacute and chronic, in addition to some clinical types with certain characteristics such as etiology and clinical manifestations.

1, acute contact dermatitis: onset more urgent. Skin lesions are mostly confined to the contact area, and a few can spread or involve the surrounding area. The typical skin lesions are clear erythema. The skin lesions are related to the contact matter. (For example, the skin lesions of the underwear dyes may be in the form of pants; if the contact is gas, dust, and lesions, it will occur in exposed parts of the body, such as the back of the hand, face, Neck, etc.), there are papules and herpes on the back. In severe cases, the redness and swelling are obvious and blisters and bullae appear. The latter's blister wall is tight and the content is clear. After the ulceration, it is erosive. Even tissue necrosis can occur. Often consciously itching or burning, after scratching, can bring the pathogenic substance to the distant part and produce similar skin lesions. A small number of patients with severe conditions may have systemic symptoms. After the contact is removed, it can be cured after 1 to 2 weeks, and the first-class temporary pigmentation. Cross-allergy, multi-valent allergy, and improper treatment can lead to recurrent episodes, prolonged unhealed or converted to subacute and chronic.

2, subacute and chronic contact dermatitis: If the contact is less irritating or lower, the skin lesions can begin to be subacute, showing mild erythema, papules, and the state is unclear. Long-term repeated exposure can lead to localized skin lesions, which are characterized by mild hyperplasia and mossy changes.

Incidence characteristics

The onset of the disease is acute, edematous erythema, papules, blister of varying size at the site of contact; blister wall tension, liquid clarification in the initial blister, pustule formation after infection; blister rupture to form erosion surface, even tissue necrosis . If the contact is gas, dust, or lesions, it occurs in exposed parts of the body, such as the back of the hand, face, neck, etc., and the dermatitis boundary is unclear. Similar dermatitis can sometimes occur due to scratching the contact with other parts of the body, such as the vulva, waist, and the like. If the body is in a highly sensitive state, the skin lesions are not limited to the contact area, and the range can be wide or even general. The symptoms are mild and itchy, and the severe ones are burning or painful. The systemic reaction has fever, chills, headache, nausea and vomiting. The course of the disease has limitations. The cause of removal can be cured after appropriate treatment for 1-2 weeks, but if it is contacted again, the allergen can be re-exposed, repeated contact, repeated attacks. If treated improperly, it can develop into subacute or chronic inflammation, and localized with mossy lesions.

Contact dermatitis examination

Skin tests are the most commonly used specific tests, including patches, scratches, spurs, and intradermal injections. It is most commonly used in clinical trials for picking and intradermal tests, such as a negative test; it can be used for intradermal test.

METHODS AND PRINCIPLES: Specific patients with specific allergens can induce specific IgE, which adheres to the IgE receptor on the surface of mast cells in the skin or submucosa, when it meets with allergens entering the body again. The bridging of one allergen with two IgE antibodies causes a series of biochemical processes in the mast cells, releasing allergic mediators, producing wheal, blushing or itching in the skin.

Diagnosis and differentiation of contact dermatitis

Diagnosis can be made based on the patient's history of exposure, lesions occurring at the site of contact and typical rash manifestations, and positive patch tests.

diagnosis

1. Have a history of exposure to irritants or sensitizers.

2. The site of the rash is often exposed to irritants.

3, the shape of the rash often varies according to the nature of the contact, such as the sensitization of the often clear edge, mainly erythema, papules, vesicles, can also occur home allergies; if the stimulus is often red, Blister or bullae, erosion, and even necrosis can occur.

4, there are itch and burning sensation, heavy pain, fever and other systemic symptoms.

5, the course of disease is self-limiting, some sensitizers can be removed after 1 to 2 weeks after removal of the cause of rash.

6, allergen skin patch test positive.

The principle of modern medical treatment of this disease is to stop contact with the sensitizing source, immediately rinse the contact area with water, apply anti-inflammatory and anti-itch topical and oral anti-allergic drugs. If necessary, add corticosteroids and use antibiotics and oral administration.

The name of non-contact dermatitis in the motherland is often named after the contact, such as "paint sore", "paste wind", "toilet sputum" and so on. Chinese medicine believes that the pathogenesis of allergic contact dermatitis is mainly due to human sputum intolerance, fur sputum is not dense, external sinister poison (contact with certain substances), toxic heat in the skin becomes sick.

Differential diagnosis

1. Acute eczema.

2. The color of erysipelas skin is bright red, the boundary of the boundary is clear, no contact history, local tenderness is obvious, accompanied by systemic symptoms such as chills, fever, headache, nausea, and peripheral blood tests often see white blood cells increase.

3 anal acute eczema

Acute eczema in any part is generally followed by flushing - papules (potular rash) - blister (exudation) - erosion - crusting (scaly) - pigmentation process, accompanied by itching, clinical manifestations of pulp exudation is obvious, serious It is dripping in a drip-like manner, and severe itching makes it difficult for patients to tolerate. Scratch, blood stasis, pustules, purulent exudation, purulent crusting, and eczema-specific appearance appear due to scratching. That is, a variety of morphological rashes exist at the same time, anal skin is a sensitive area, acute eczema itching is particularly intense, fecal contamination is more likely to cause bacterial infection, symptoms are more severe, can expand and perineum, scrotum, buttocks skin, affecting patients' lives and work, so that The course of the disease is extremely unstable, the treatment process is prolonged, and it becomes a chronic process.

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