**3. Special types of contact urticaria**

#### **3.1. Occupational contact urticaria**

Skin diseases are the second most common occupational diseases in Europe and occupational contact urticaria (OCU) makes up 1–8% of occupational skin disorders [12]. The most commonly affected professional groups are healthcare employees, food handlers, farmers and hairdressers [24, 25]. Immunologic and non-immunologic contact urticaria types can be seen in OCU. The risk of sensitization against all proteins is high in presence of atopy in OCU [10]. Besides, atopy is also important in OCU associated with NICU [10].

Natural rubber latex is the most commonly identified allergen and this allergy is seen in 1–3% in general population and 5–10% of healthcare workers in Europe [10]. *H. brasiliensis* proteins are the main responsible agents for natural rubber latex allergy [10]. A reaction against modified proteins (wheat, soy and Croetin Q) that are added to shampoo and especially ammonium persulfate is often observed in hairdressers [26, 27]. Reactions against saliva, amniotic fluid, urine and seminal fluid of animals have been defined in animal handlers, farmers and veterinarians. Dyes cause contact urticaria at significant levels in the cosmetic and industrial sectors [4, 6].

#### **3.2. Oral allergy syndrome (food contact dermatitis)**

"Oral allergy syndrome" is used to identify ICU developing in the mucosa [28]. It is characterized by mucosal edema, itching and a burning sensation after contact of the oral mucosa with respiratory allergens [29]. Cross-reactivity between homologous pollen and food allergens is accused in the etiology [29]. The term pollen-food allergy syndrome (PFAS) can therefore also be used [30].

Fruits and vegetables especially apples, carrots, tomatoes, pears, cherries, plums, celery, spices and hazelnuts are the agents that are often blamed for the oral allergy syndrome. The individuals who have oral allergy syndrome frequently suffer from atopy and pollen allergy, therefore a cross allergy against IgE antibodies has been observed [30].

#### **3.3. Physical contact urticaria**

Some physical urticaria cases occur following skin contact with hot, cold, light (UV: solar urticaria), water or as dermographism, pressure hives and vibratory angioedema. A physical agent does not cause a reaction alone but leads to the activation of a chemical product in some cases. It is possible to see this mechanism in induced contact urticaria. Benzophenones, chlorpromazine, methenamine hippurate and formaldehyde are included among the agents that can cause such a reaction [31–33].

#### **3.4. Delayed and prolonged contact urticaria**

Contact urticaria, protein contact dermatitis and allergic contact dermatitis can sometime coexist. The patients can primarily present with an urticarial lesion and the contact dermatitis and eczematous lesions can develop later [32, 34]. Elm, vaseline and castor oil are agents that often cause delayed and prolonged contact urticaria [10].
