Nickel and cobalt allergy before and after nickel regulation--evaluation of a public health intervention.

Over the 20th century, the frequent use of nickel in consumer products resulted in an increasing prevalence of nickel allergy. Risk items included suspenders in the 1950s-1960s; buttons, zippers and rivets in the 1970s; and ear-piercing jewellery in the 1980s. When subjects allergic to nickel were exposed to nickel in high concentrations, it often resulted in allergic nickel contact dermatitis and hand eczema. In 1990, the Danish government began to regulate consumer nickel exposure as a response to the increasing nickel allergy problem. In 1994, the EU Nickel Directive was passed, a regulation that was based on the Danish and Swedish nickel regulations. These major public health interventions were expected to change the epidemiology of nickel allergy and dermatitis in Europe. Furthermore, it was debated whether nickel would be replaced by cobalt in inexpensive jewellery and result in higher prevalence of cobalt allergy. An evaluation of the possible effects of the European nickel regulations is of importance to ensure protection of consumers and dermatitis patients. This doctoral thesis aimed to evaluate the effects of regulatory interventions on nickel exposure by investigating the development of nickel allergy and dermatitis before and after nickel regulation. Furthermore, a change in the association between nickel allergy and hand eczema was evaluated. The nickel spot test was validated to determine its value when used for screening purposes. Possible explanations for the persistence of nickel allergy were explored including genetic predisposition and consumer nickel exposure from jewellery and accessories. A cobalt spot test was developed and validated. Finally, it was evaluated whether a cobalt allergy epidemic had replaced the nickel allergy epidemic after nickel regulation in terms of increasing cobalt sensitization and cobalt exposure. The thesis showed that the prevalence of nickel allergy decreased significantly after nickel regulation in young Danish women from the general population (18-35 years) and in young Danish female dermatitis patients from a university patch test clinic (0-30 years). Stratification by ear-piercing status revealed that women ear pierced before 1990 had a significantly higher prevalence of nickel allergy and dermatitis than women ear pierced after 1990. Furthermore, the association between hand eczema and nickel allergy decreased in young women aged 18-35 years when a comparison was made between women who were patch tested and questioned in, respectively, 1990 and 2006. Despite the decreasing prevalence of nickel allergy, this condition remains prevalent in young Danish women, as about 10% are nickel allergic. Genetic predisposition to nickel allergy was evaluated by investigating the possible association between filaggrin null mutation status and nickel allergy. A positive association was found but it was also concluded that environmental nickel exposure is of much greater importance. Thus, of 354 consumer items purchased from 36 different stores in Copenhagen, 22% released nickel in concentrations that may result in nickel dermatitis in sensitized subjects. Therefore excessive consumer nickel exposure remains common in Denmark and may be an important explanation for the persistence of nickel allergy. Excessive nickel release was also frequent when samples of earrings purchased in Warsaw and London were examined with the nickel spot test, in particular earrings purchased from street markets and shops with independent ownership. Only very weak indications of an emerging cobalt allergy epidemic were found, as the prevalence of cobalt allergy has not yet increased in young people and only four of 354 consumer items purchased in Copenhagen released cobalt in concentrations that may result in cobalt dermatitis in sensitized individuals. The specificity of the nickel spot test was 98% and the sensitivity 59%. Also, a cobalt spot test was developed and validated and seemed to be a useful diagnostic tool. In conclusion, the Danish nickel regulation and the EU Nickel Directive have changed the epidemiology of nickel allergy in Denmark. However, the Nickel Directive and its reference methods need to be revised to better protect consumers and dermatitis patients.