Babies develop allergies primarily because their bodies are still developing, leading to increased absorption of potential allergens and a less mature immune response.
During early life, immature mucosal defenses permit the increased absorption of allergens, which then act on an immature immune system. This means the protective layers lining a baby's digestive system and airways aren't as robust as an adult's. Consequently, more allergy-triggering substances (allergens) can pass through these barriers into the body. Once inside, these allergens interact with an immune system that is still learning what is harmless and what is a threat. This interaction can sometimes lead the immature immune system to wrongly identify the allergen as dangerous, triggering an allergic reaction.
How Allergies Develop in Infants
The process involves a combination of factors unique to a baby's early stage of development:
- Immature Mucosal Barriers: The lining of the gut, for instance, is more permeable in infants. This allows larger protein molecules from foods to pass into the bloodstream more easily.
- Immature Immune System: A baby's immune system hasn't fully developed its ability to distinguish between harmful pathogens and harmless substances like food proteins or pollen. When it encounters an allergen, it might mount an inappropriate defense response.
This combination makes babies more susceptible to developing sensitivities that can later manifest as allergic reactions.
Common Allergens in Infancy
In infants, the main exposure is typically to food allergens. As children get older, exposure shifts more towards inhalant allergens like pollen or dust mites.
Some common food allergens for babies include:
- Cow's milk
- Eggs
- Peanuts
- Tree nuts
- Soy
- Wheat
- Fish
- Shellfish
Understanding this developmental vulnerability helps explain why introducing foods and managing environmental exposures in early life are crucial topics for parents and healthcare providers.
