Introduction
Allergic diseases have been increasing in the last decades, particularly in developing countries 1. This increase is likely a consequence of environmental factors that heightens the risk of allergic diseases in genetically susceptible individuals 2. To date, allergy birth cohort studies are from western countries3,4 and modern Asian countries 5-8. The generalizability of these results to the context of developing Asian countries may not be relevant since the environment, feeding patterns and lifestyles are largely different.
Positive family history of atopy is one of the important predisposing factors of allergic diseases 9,10. Maternal atopy is associated with allergic diseases than paternal influence11. The protective effects of breast feeding against allergy remain a debating issue 12. Environmental factors related to hygiene hypothesis theory, such as high socioeconomic status, extended family, antibiotics exposure during infancy period, farm environment and household furry pets, have been proposed to be associated with allergic diseases 13. The rationale behind this theory is that families with hygienic lifestyles are less exposed to microorganisms. So the immature immune system of the young infants might be driven towards allergic inflammation.
The atopic march refers to the progression of allergic diseases during infancy and childhood 14. Classically, the atopic march begins with atopic dermatitis (AD) or food allergy (FA) then progresses to asthma or allergic rhinitis (AR) 14. The co-occurrence between the diseases are also common15,16. These data support the existence of a shared set of polymorphisms in allergic patients. However, previous literature has shown that only one-third to half of the subjects with AD and FA developed atopic march later in life 17. Besides, not every subject with asthma and AR preceded with AD or FA17.
Using a population-based birth cohort manner, our study aimed to describe the incidence, and natural course including of atopic march and to identify factors associated with allergic diseases in Thai population, which reflects developing Asian countries.