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PRIMARY IRRITANT DERMATITIS
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Many irritants cause damage by exhausting the horney layer, denaturating keratin and altering the water holding capacity leading to physio-chemical changes of the skin. Repeated exposure with the irritating substance which have an irritant must exceed a certain threshold to cause an allergic reaction. Allergic contact dermatitis is due to repeated exposure of the skin to a substance, which can‘t at the beginning cause irritation or eczematization. Repeated exposure with such substance may cause contact dermatitis. Primary irritant dermatitis due to primary irritating factors is not an allergic reaction, and must be differentiated from allergic contact dermatitis . Primary irritants may cause non-allergic inflammatory reaction on the first time the skin is exposed to that specific substance. The severity of the reaction depends on different factors, mainly the concentration of the substance , duration of exposure and the local conditions of the skin. Primary irritant dermatitis is common in infants and young children. Mild and simple substances such as soaps and even saliva may cause irritation in infants but may have no effect on older children . Different primary irritants that may cause direct non-allergic reaction are: Detergents , cosmetics ,chemicals. Plants , shrub, grasses as in poison ivy , oak and others. Metals : nickel, dichromate in jewellary.
Paraben: used in cosmetics , creams and preservatives. Paraphenylenediamine. Antibiotics : neomycin. Local anesthetics : benzocaine. Antihistamine and even topical corticusteroid preparations . Colophony : in plasters and collodium. Balsam of Peru : in perfumes and citrus fruits .
Fig. 173b.Primary irritant
dermatitis (Perfumes)
Fig.173d. Primary irritant dermatitis(Stockings)
Wood alcohol : in cosmetics , creams and lanolin .. Rubber and plastic : in clothing , shoes and gloves . Alkalis: Such as soaps, shampoos and detergents containing sodium, potassium, ammonium and calcium hydroxides , which are used for the manufacture of detergents . Plastic and other synthetic materials Diapers are a common cause of napkin dermatitis. Toilet seats or plastic pants of polyester may cause primary irritant dermatitis . Acids : such as carbolic acid ( phenol) may cause primary irritant dermatitis or even fatal toxic effect especially in infants and young children . Other acids as salicylic, sulfuric, nitric, ionic, tannic may cause severe burn when it is concentrated. Treatment of such cases is by immediate rinsing with water and sodium bicarbonate or soap . Gases and dust especially in hot humid climate . Insect repellents, air fresheners, domestic pets as dogs, cats, birds, plants, roses and many others. Different irritants causing contact dermatitis in different sites: Scalp and face : Hair dyes, hair spray, shampoos, and cosmetics . Perioral: Citrus fruits such as orange, lemon, apple coming in direct contact with the skin, chewing gums and tooth paste . Eyes : Mascara, volatile gases, false eyelashes and cement . Nails : Nail polish . Hands : Contact with different irritants such as soaps, detergents, plastic gloves, perfumes, orange, lemon juice and peel, onion, garlic and vegetable juices coming in direct contact with the skin. Crural and napkin areas : Napkins, soaps, perfumes, topical preparations either powders, medicaments or cosmetic preparations . Trunk and abdomen : Synthetics as wool , silk, polyester, dyes, chemicals perfumes or metals in trousers and brassieres. Lower limbs : Shoe dermatitis due to leather , plastic or from dyes and chemicals used during manufacture . Socks of wool or polyester or walking bare-footed especially on the woolen and polyester rag or carpets may provoke irritant dermatitis . The most common clinical patterns of primary irritant dermatitis seen in the newborn are perianal dermatitis and napkin dermatitis . Clinical features of primary irritant dermatitis Primary irritant dermatitis may present with acute erythema, swelling of the skin followed usually by vesiculation and oozing. Crusted scaly surface develops in later stage.
In the chronic stage the skin becomes thick, hyperpigmented and lichenified.
Fig.173g. Chronic dermatitis
Itching is the main symptom of dermatitis and varies according to the irritant, stage, age and the patient‘s threshold . Secondary infection is common due to excoriation by severe itching. Diagnosis Patch test is sometimes very helpful to spot the offending factor . It is important to note that patch test should not be done in severe and extensive dermatitis until controlling of the lesion especially in patients who are extremely sensitive. Meanwhile, when doing patch-test care should be taken that the patient is not under corticosteroids or antihistamine especially the long acting ones, where these may lead to inaccurate interpretation . Strong testing materials in patch test should be diluted in order not to cause direct sensitization or exacerbation of the primary lesions .
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