① There is no allergic reaction mechanism involved, but the result of direct irritation caused by the strong irritation/toxicity of the contact object;

②With sufficient concentration and sufficient exposure time, it can happen to anyone;

③There is no certain incubation period;

④Skin lesions are mostly limited to direct contact parts and have clear boundaries;

⑤Skin lesions can subside after contact is stopped

① The contact object (hapten) itself is non-irritating, and there are usually no adverse reactions after skin contact with it; however, a small number of people with special allergies will be exposed to the same allergen again after a certain incubation period (4~20 days) after exposure. In some cases, allergic inflammation (usually type IV hypersensitivity) may occur in the skin and mucous membranes at the contact site; in some cases, the allergic reaction becomes lighter and lighter due to repeated long-term exposure, so that no reaction occurs again (hardening). Phenomenon);

② Skin lesions are often widespread and symmetrically distributed;

③Easy to relapse;

④Skin patch test positive

A small number of chemicals can cause dermatitis only after being exposed to a certain amount of sunlight (ultraviolet) after contacting the skin; among them, when the skin is exposed to a certain amount of photosensitizer (such as psoralen) and then exposed to an appropriate amount of light, it can occur in everyone Phototoxic reaction (called "phototoxic contact dermatitis"); photosensitivity reaction involving the immune system is called "photoallergic contact dermatitis"

The onset is rapid; skin lesions are mostly limited to the contact area

Typical manifestations: well-defined erythema, the shape is related to the contact object; there are papules/papu herpes on it. In severe cases, the redness and swelling are obvious and blisters/bullae appear. The blister wall is tense and the content is clear. After ulceration, it will appear erosive. Occasionally, it may occur. Tissue necrosis; conscious itching/burning pain, scratching can cause similar skin lesions in remote areas, and a few may have systemic symptoms; after removing the contact object and actively treating it, it can usually be cured within 1 to 2 weeks, but temporary pigmentation may be left behind

The irritation of the contact substance is weak/the concentration is low; it manifests as mild erythema and papules with unclear boundaries.

Long-term and repeated exposure can make local skin lesions chronic; manifested as mild hyperplasia of skin lesions and lichen-like changes.

Cosmetic dermatitis: acute, subacute and chronic dermatitis caused by contact with cosmetics/hair dyes

Diaper dermatitis (napkin dermatitis, diaper dermatitis): due to diaper irritation (especially enzymes in feces), erythema, papules, papule herpes or erosions appear on the diaper contact parts (buttocks, vulva, thighs) of infants and young children; the boundaries are clear, The shape is consistent with the diaper bandaging range; it is prone to secondary candida and bacterial infections, which can occur repeatedly

Paint dermatitis: skin sensitization caused by paint or its volatile gases, mostly involving exposed parts

Airborne contact dermatitis: Inflammation of exposed areas (e.g., upper eyelids, face) caused by chemical suspensions in the air (e.g., sprays, perfumes)

Sponge formation in the epidermis; dilation of superficial dermal capillaries and perivascular lymphocyte infiltration

Hyperkeratosis/parakeratosis, obvious hypertrophy of the spinous layer, thickening of capillary walls in the superficial dermis, and thickening of collagen fibers

It often appears rapidly and symmetrically; on the basis of diffuse flushing and mild edema, dense, miliary-sized papules/papule vesicles/small blisters appear, often merging into sheets with unclear boundaries, with much exudation, and then erosion and scabbing. ; accompanied by severe itching, especially at night

Vigorous scratching, drug abuse, and hot water washing can aggravate the condition and even lead to secondary infection, causing pustules, pustules, lymphadenopathy, fever, and herpetic eczema; it can subside after appropriate treatment, or it can evolve into subacute Or chronic eczema (which can recur acutely after stimulation by external and internal factors)

It usually develops over a long period of time after the inflammation of acute eczema is reduced or improperly treated.

Manifestations: Redness, swelling and oozing are reduced, but there are still a small number of small papules/papule herpes, accompanied by erosion, scabs and scales, and itching is still obvious; the course of the disease can last for several weeks, and can be acute, and can become chronic if it does not heal.

Mostly caused by acute or subacute eczema; mostly limited to hands, feet, calves, thighs, vulva and perianal area

Manifestations: hypertrophic infiltrative patches with clear borders, some parts of which may have lichen-like changes, and obvious pigmentation (note: the Human Health Edition textbook believes that there may also be hypopigmentation), with small papules scattered around; paroxysmal severe itching, due to Scratches, erosion, oozing, and bloody scabs may appear due to scratching; the course of the disease may last several months or years, and acute attacks may occur after stimulation.

limitation

Generalized

Avoid various external stimuli (such as scratching, scalding, soap scrubbing, drug abuse); keep the skin clean; prevent secondary infections

Antihistamines: most commonly used

Obvious exudation: antifibrinolytic agents (such as 6-aminocaproic acid) can be taken

Chinese herbal medicine: mainly clearing heat, removing dampness, cooling blood and dispelling wind

Glucocorticoids: Generally not suitable for use

Drug treatment: Coal tar, glucocorticoids, antibiotics and antifungal drugs are commonly used; different drugs and dosage forms are selected according to the type of skin lesions.

Physical therapy: phototherapy (UVB), hydrotherapy; used for chronic localized eczema when other treatments are ineffective.

Use when necessary

1. Acute urticaria: often caused by IgE-mediated type I hypersensitivity reaction, including immediate phase (mainly mediated by histamine) and delayed phase (mainly mediated by LT); the causative agent is easy to find, Common ones such as food, drugs, and infections can be whole antigens or haptens; physical factors can also induce

2. There are also urticaria mediated by type III hypersensitivity reaction (often accompanied by vasculitis) and urticaria mediated by non-immune mechanisms.

acute

Chronic

physical

special

1. Papular urticaria (urticarial papulosa)/acute simple prurigo: a wheal with papules/small blisters in the center and obvious itching; more common in children, mostly related to insect bites

2. Urticarial vasculitis

3. With abdominal pain: surgical acute abdomen

4. Accompanied by obvious fever: drug rash, accompanied by other infections

Cause treatment

Systemic drugs

topical medications

desensitization treatment