Introduction

Atopic dermatitis (AD) occurs in individuals who have a genetic predisposition and have been exposed to certain environmental influences. It is the most prevalent chronic inflammatory skin disease in childhood (Ruzicka et al., 1991). As pointed out in earlier chapters there is good evidence that this condition has significantly increased over recent decades. However, it is still unclear which factors are responsible for the increase. For AD the role of genetic predisposition to the disease is well established (Niermann, 1964; Schultz Larsen et al., 1986; Küster et al., 1990). Within the multifactorial pathogenesis several contributing external factors have been described. In addition to sex (Engbak, 1982; Erisson-Lihr, 1955; Larsson & Liden, 1980) and age (Rajka, 1989), psychosomatic influences (Young et al., 1986), exposure to aeroallergens (Vieluf et al., 1993) and food allergens (Przybilla & Ring, 1990), climatic stimuli (Young, 1980), and socioeconomic status (Williams et al., 1994) have been linked to AD. However, the postulated increase cannot be explained totally by these risk factors. Environmental contaminants and, in particular, air pollutants have been suspected as factors which possibly aggravate AD (Ring, 1991; Ring et al., 1995). The biological plausibility of this suggestion arises from the fact that most air pollutants act as nonspecific irritants as well as immunomodulators, e.g. enhancing IgE formation in animals (Behrendt et al., 1991; Suzuki et al., 1989; Takafuji et al., 1989).