(HealthDay) -- Eczema, asthma, and rhinitis affect more than 50 percent of children up to age 12, according to a study published online Feb. 16 in Allergy.

Natalia Ballardini, Ph.D., of the Karolinska Institute in Stockholm, and associates conducted a to evaluate the development and comorbidity of , asthma, and rhinitis in relation to sex and parental allergy in a population-based group of 2,916 children at ages 1, 2, 4, 8, and 12 years.

Using parental , the researchers found that, at 12 years, 58 percent of the children had had eczema, asthma, and/or rhinitis at some point. At 12 years, 7.5 percent of all children were affected by at least two allergy-related diseases, with comorbidity increasing with age. Parental allergy correlated with more persistent disease and comorbidity, and was associated with an elevated risk of having any allergy-related disease up to age 12 years (adjusted odds ratio, 1.76). Throughout childhood, there was an increased risk for males. There was no gender difference for disease persistence and only minor for comorbidity.

"Allergy-related diseases may affect a majority of children. Eczema, asthma, and rhinitis develop dynamically throughout childhood, and allergic comorbidity is common. These findings indicate that allergy-related diseases should be neither seen nor studied as isolated entities," the authors write.