**2. Epidemiology (prevalence and incidence)**

Previously, ACD was once wrongly considered uncommon in the pediatric population (Hjorth, 1981). It was thought that children had reduced exposure to contact allergens during childhood. The second reason was less susceptibility of the child immune system to contact allergens (Mortz & Andersen, 1999). However, during the last 10-20 years, several reports have described a considerable number of children with CA and ACD (Pevny et al., 1984a; Pevny et al., 1984b; Weston & Weston, 1984; Rademaker & Forsyth, 1989; Barros et al., 1991; Dotterund & Falk, 1995; Motolese et al., 1995; Katsarou et al., 1996; Rudzki & Rebandel, 1996; Stables et al., 1996; Manzini et al., 1998; Brasch & Geier, 1997), confirming that CA and ACD may be frequent in children and may cause significant problems. Prevalence of positive patch tests without clinical correlation (CA) in population-based studies is different from the prevalence of ACD (positive patch test with clinical correlation) in patients referred for patch testing.

Allergic Contact Dermatitis in Children 113

Sensitization to contact allergens begins in infancy and continues to be more common in toddlers and young children (Seidenari et al., 1992; Giordano-Labadie et al., 1999; Vozmediano & Hita, 2005; Militello et al., 2006; Clayton et al., 2006; Garg et al., 2009; De Waard-van der Spek & Oranje, 2009), the age of sensitization can occur very early. In study of Bruckner et al. (Bruckner et al., 2000), 45% of patients with positive reactions were younger than 18 months. Even neonates may be sensitized (Fisher, 1994a; Bruckner et al., 2000). Fisher (Fisher, 1994a) reported a 1-week-old infant with strongly positive patch test reaction to epoxy resin, manifesting as band-like dermatitis above the wrist because of vinyl band that was made of an epoxy resin. A 7-month-old child has revealed ACD from nickel– plated snaps on the back (Fisher, 1994a). Motolese et al. (Motolese et al., 1995) studied 53 infants (3 months to 2 years) with dermatitis and patch tested them. Positive patch tests were seen in 32 (60%) and 20 out of the 32 sensitized infants had clinically relevant contact allergies. Hjorth (Hjorth, 1981) thought that patch test reactions in infants were predominantly irritant reactions, especially when testing with nickel sulfate. In a study of Jøhnke et al. (Jøhnke et al., 2004) it was confirmed that increasing numbers of infants positively patch tested to nickel sulfate but most reactions were transient and probably irritant or non-specific nature. Experimental CA to plants of the *Rhus* genus has also been induced in infants, showing that sensitization is possible (Epstein, 1961). Manzini et al. (Manzini et al., 1998) reported that the highest sensitization rate was noted in children aged up to 3 years. It is still unclear why some sensitivities, for example nickel, are prevalent in the young but less common in the old. Possible explanations include changing trends in exposure to nickel (i.e. increased use of imitation jewellery and different frequencies of ear piercing in different generations) or loss of clinical allergy because of avoidance, induction of tolerance, or inability to mount an immune response despite continuing exposure (Garg et al., 2009). Recall studies showed persistence of CA to nickel after 8 years in 79% and 60% to other allergens (Nielsen et al., 2001; Garg et al., 2009). Others found that lanolin, only 41% had persistent allergy at 5 years (Carmichael et al., 1991). The increase in fragrance allergy with age may be because of cumulative exposure to toiletries and increased use of

The relationship between CA and atopy is frequently discussed and still not settled (Rystedt, 1985; Schnuch et al., 2006). Several studies have been performed in children with suspected CA or suffering from AD or chronic dermatitis. Patch testing in symptomatic children with dermatitis has revealed positive reactions in 15% to 52% of subjects (Rademaker & Forsyth, 1989; De Groot, 1990; Katsarou et al., 1996; Rudzki & Rebandel, 1996; Stables et al., 1996; Shah et al., 1997; Vozmediano & Hita, 2005; Goossens & Morren, 2006; Wahlberg & Lindgerg, 2006). Some authors have indicated that ACD is less prevalent in patients with AD (Uhr, 1960; Rystedt, 1985; De Groot, 1990; Katsarou et al., 1996; Stables et al., 1996; Brasch & Geier, 1997). Several authors were unable to detect differences between atopic and nonatopic subjects in this regard (Marghescu, 1985; Pambor et al., 1991; Goossens et al., 1995; Akhavan & Cohen, 2003; Beattie et al., 2007; Milingou et al., 2010). Against this others have even found a greater prevalence of ACD in patients with AD (De la Cuadra et al., 1990; Lammintausta et al., 1992; Dotterund & Falk, 1995; Lugovic & Lipozencic, 1997; Giordano-Labadie et al., 1999; Clayton et al., 2006). A higher prevalence of CA in AD could

**2.4 Prevalence related to age** 

medicaments (Garg et al., 2009).

**3. Contact sensitisation and atopic dermatitis** 

#### **2.1 Prevalence of contact allergy in a selected population**

Patch test studies in series of selected children with suspected ACD have reported frequencies of positive reactions varying from 14% to 71% of patients. Of these, about 56- 93% was of current relevance (Weston & Weston, 1984; Pevny et al., 1984b; Fisher, 1994a; Rudzki & Rebandel, 1996; Stables et al., 1996; Manzini et al., 1998; Bruckner et al., 2000; Machovcová et al., 2001; Wöhrl et al., 2003; Heine et al., 2004; Lewis et al., 2004; Jøhnke et al., 2004; Vozmediano & Hita, 2005; Wahlberg & Lindberg, 2006; Goossens & Morren, 2006; Jacob et al., 2008). Among the children with a positive patch test 3.2% to 54.4% had multiple contact allergies (Mortz & Andersen, 1999).
