Children exposed to higher levels of cat allergen in their first 2 years of life may be at greater risk of becoming allergic to the animals, a new study from Germany shows. However, the risk of sensitization at 6 years old seems to disappear.

The findings show that avoiding exposure to cats at home might not be enough to protect some children from becoming allergic, Dr. Joachim Heinrich of the GSF-National Research Center for Environment and Health in Nuremberg and colleagues conclude.

Some studies have shown that having pet cats in early life increases the risk of developing a cat allergy, while others have found owning cats actually protects against cat allergy, the researchers note.

Because most studies have looked at only one point in time, Heinrich and his team followed a group of 2,166 children from birth to age 6. When the children were 3 months old, the researchers collected samples of dust from their homes. At 2 and 6 years of age, children had blood tests and house dust was sampled again.

The higher the levels of cat allergen in house dust when the children were 3 months old, the more likely they were to have developed sensitization to the allergen by 2 years of age, the researchers found. Sensitization to an allergen does not mean a child will go on to become allergic to it, they note, although it does indicate a child is at increased risk.

But by age 6, the researchers found no correlation between cat allergen exposure in infancy and sensitization to the allergen or the presence of any type of allergic symptoms or disease.

Heinrich and his team did find that total cat exposure over time, defined as the presence of a cat in the home and how frequently he or she had contact with cats outside the home, increased the likelihood of sensitization among children up until age 6.0. Children who didn’t have cats at home but were frequently in contact with the animals were at particularly high risk of developing sensitization, especially if their parents had any type of allergic disease.

In a press release accompanying the study, Heinrich notes that family history of allergic disease remains the most important factor in whether a child will go on to develop allergies. Parents of these at-risk kids should not have cats in the home, and should try to avoid exposure to the animals outside the home, he says, but this still may not be enough to prevent children from becoming sensitized to cat allergens.

SOURCE: Journal of Allergy and Clinical Immunology, May 2007.