Exposure to indoor allergens in early infancy and sensitization

Indoor allergens play a major role both in sensitization and as triggers of asthma in children. The relationship between allergen exposure and sensitization to cats, dogs, and mites was studied prospectively in 100 newborn babies with a history of allergy in both parents.

Skin prick tests were done with Dermatophagoides pteronyssinus, D.farinae, and cat and dog allergens in all the children at 6 and 18 months of age and in 86 children at 5 years of age. Dust samples were collected from the homes during infancy and at 5 years. The parents of the children responded to a questionnaire focused on environmental factors that could influence indoor allergen levels. In addition, dust samples were collected from the day-care centers of the sensitized children. The allergen levels were determined by ELISA.

The levels of the major cat allergen, Fel d 1, varied from 0.02 microg to 6.8 microg/gm (geometric mean [GM], 0.4 microg/gm) during infancy and less than 0.02 microg to 13 microg/gm dust (GM, 0.12 microg/gm) at age 5 years. Dog allergen, Can f 1, levels ranged from 0.18 microg to 590 microg/gm (GM, 3.1 microg/gm) in infancy and 0.09 microg to 13 microg/gm at age 5 years (GM, 0.6 microg/gm). Eleven children (13%) were sensitive to cats, and three were sensitive to dogs at 5 years of age. They had been exposed to similar levels of allergen as the nonsensitized children. The levels of mite allergen (Der p 1 + Der f 1) at age 1 year varied from less than 0.02 microg to 1 microg/gm dust (GM, 0.12 microg/gm) and at age 5 years from less than 0.02 microg to 3.5 microg/gm (GM, 0.05 microg/gm) dust. Only two homes contained mite allergen levels greater than 2 microg/gm dust. The levels were less than 0.3 microg/gm dust in all but one sample from the day-care centers. Only one child was sensitized to mites at age 5 years. The mite allergen level was less than 0.1 microg/gm at home, and he did not attend a day-care center.

The findings indicate that exposure to low levels of indoor allergens in early childhood is associated with a low incidence of sensitization. However, levels well below currently suggested threshold levels may cause sensitization in children with a family history of allergy. We suggest that a fixed threshold risk level for allergic sensitization may not be appropriate in all climates.