Contact dermatitis is an acute or chronic inflammatory reaction that occurs at the site of skin-mucosal contact due to exposure to certain exogenous substances. The etiology can be divided into primary irritants and contact sensitizers depending on the pathogenesis. Some substances can be sensitizers at low concentrations and irritants or toxic substances at high concentrations.
1.Primary irritant reaction
The contact substance itself has strong irritation (such as contact with strong acids, strong bases and other chemicals) or toxicity, and anyone exposed to the substance can develop the disease. Some substances are less irritating, but a certain concentration of exposure to a certain period of time can also cause disease.
The common features of this type of contact dermatitis are.
(1) Anyone can develop the disease after exposure.
(2) No certain incubation period.
(3) The lesions are mostly limited to the site of direct contact and are well defined.
(4) after the cessation of contact lesions can subside.
2.Contact sensitization reaction
It is a typical type IV allergic reaction. Most people do not develop the disease after contact, but only in a few people, after a certain period of incubation, the skin and mucous membranes of the contact area become inflamed with allergic reactions. Langerhans cells carry this complete antigen to the epidermal-dermal junction and sensitize T-lymphocytes with an induction period of about 4 days. When the sensitized individual is re-exposed to the sensitizing factor, he or she enters the excitation phase, which generally produces a significant inflammatory response within 24-48 hours.
The common features of this type of contact dermatitis are.
(1) There is a certain latency period, no reaction occurs after the first exposure, and the disease develops only after 1-2 weeks if the same sensitizer is re-exposed.
(2) The lesions are often widespread and symmetrically distributed.
(3) Recurrence is easy.
(4) Positive patch test.
Possible sources of common contact sensitizers: leather products, costume jewelry, cement, industrial pollutants, fungicides, rubber products, hair dyes, fur and leather products, pigments, pigment thinners, solvents, facial tissue, textiles, cosmetics, shampoos, industrial, nail polish, dentures, synthetic resins, soaps, detergents, insecticides.
Clinical manifestations
The disease can be divided into acute, subacute and chronic according to the course of the disease, in addition, there are some clinical types with certain characteristics in terms of etiology and clinical manifestations.
1. Acute contact dermatitis
The onset of the disease is acute. The lesions are mostly confined to the contact area, but a few can spread or involve the surrounding areas. The typical lesion is a well-defined erythematous plaque, and the shape of the lesion is related to the contact material (e.g., the lesion can be trouser-shaped distribution if the underwear dye allergy, and diffuse distribution of the lesion on the exposed parts of the body if the contact material is gas or dust), with papules and papules, and in severe cases, redness and swelling are obvious and blisters and blisters appear, and occasionally tissue necrosis may occur. Itching and burning pain are often perceived, and scratching may carry the causative material to distant sites and produce similar lesions. A small number of patients with severe disease may have systemic symptoms. Cross-allergy, polyvalent allergy and improper treatment may lead to recurrent, prolonged or subacute and chronic attacks.
2, subacute and chronic contact dermatitis
If the irritation of the contact is weak or the concentration is low, the lesions can be subacute at first, manifesting as mild erythema and papules with unclear boundaries. Long-term repeated exposure can lead to chronic local lesions, manifested as mild hyperplasia and mossy lesions.
3, special types of contact dermatitis
(1) Cosmetic dermatitis: acute, subacute or chronic dermatitis caused by contact with cosmetics or hair dyes. The severity of the disease varies, the lighter for the contact site appears red, papules, papules, the heavier can appear on the basis of erythema blistering and even generalized.
(2) diaper dermatitis: diaper change is not diligent, ammonia-producing bacteria decomposition of urine produces more ammonia to stimulate the skin. It mostly affects the perineum of the infant and sometimes spreads to the groin and lower abdomen. The lesions are large and flushed, and macules and papules with clear edges may occur.
(3) Lacrimal dermatitis: skin sensitization caused by paint or its volatile gases, mostly involving exposed areas. It manifests as flushing, edema, papules, papules, blisters, and in severe cases may fuse into large blisters. Itching and burning sensation are felt.
The patch test is the simplest and most reliable method to diagnose contact dermatitis.
The principles of treatment for this disease
Search for the cause, rapid removal from the contact and aggressive symptomatic treatment. After treatment of allergic reactive contact dermatitis, re-exposure to the allergen should be avoided to avoid recurrence.
Dyed hair dermatitis
For those who have recurrent attacks and persistent problems, do not wash your hair during the onset of the disease, and wash your hair less often after it is cured. It is likely that you will wash your hair once (each time you wash your hair, the hair dye will melt some) and have an attack. When washing your hair, avoid water flow and other parts of your body, dry your hair immediately after washing, blow dry with a hair dryer, and if necessary, cut your hair bald. Avoid dyeing hair again after healing!