INTRODUCTION
Allergy is a hypersensitivity reaction initiated by immunologic mechanisms.1 The prevalence of allergic diseases is increasing worldwide, including in Japan. The 1999 International Study of Asthma and Allergies in Childhood (ISAAC) reported that the prevalence of atopic dermatitis ranged from <2% in Iran to >16% in Japan and Sweden among children aged 6-7 years.2 Phase III of the same study completed 7 years later reported an increase in the prevalence of asthma, rhinoconjunctivitis, and eczema in many countries; a decrease in prevalence was reported only for asthma among adolescents aged 13-14 years.3
Previous studies have reported a relationship between childhood attention-deficit hyperactivity disorder (ADHD) as well as other mental health problems and allergy. Studies have shown that children with eczema or atopic dermatitis achieved higher scores on the Strengths and Difficulties Questionnaire (SDQ), indicating that the presence of eczema may be associated with worse mental health.4-7 Similar findings have been reported for conditions such as ADHD and autism spectrum disorders (ASD) among children with eczema. Children with atopic dermatitis have been shown to be at increased risk of ADHD or ASD. 8-13
Similar associations have been reported for asthma and rhinitis5. A systematic review has found that children with ADHD had a higher rate of asthma than those without ADHD.14 A separate meta-analysis suggested that patients with asthma, particularly those with severe symptoms, should be considered at higher risk of behavioral difficulties that may necessitate psychosocial interventions.15 In a nationwide population-based prospective study, Chen suggested that asthma was a risk factor for further development of ADHD. In addition, asthma in very early life has been shown to increase the risk of developing ADHD during school years.16 Suwan reported increased rates of allergic sensitization in ADHD cases.17 The prevalence of allergic rhinitis among children with ADHD has also been reported as higher than that among children without ADHD.17 A study based on the Taiwan National Health Insurance Research Database reported that allergic disorders, in particular, bronchial asthma and allergic rhinitis, but not atopic dermatitis, were risk factors for ADHD18.
This evidence notwithstanding, previous studies on the relationship between allergic symptoms and childhood behavioral problems often failed to consider the impact of parental factors associated with children’s psychosocial development. A study by Tokunaga et al. examined the impact of parenting stress in this context and found that paternal stress was significantly associated with the risk of child hyperactivity/inattention, while maternal stress was significantly associated with difficulties in peer relationships and emotional symptoms.19 However, it is plausible that parenting stress is the effect, not the cause, of childhood behavioral problems, resulting in poorer SDQ scores.. It is also plausible that this relationship is bi-directional.
This study aimed to investigate the relationship between allergic symptoms and children’s behavioral problems, adjusting for potential confounding factors such as demographic characteristics, parenting stress, and allergy-related variables.