The immune system protects the body against viruses, bacteria and fungi by releasing powerful chemicals and proteins that destroy these harmful substances and microbes. However, the immune system of a toddler with allergies will react abnormally to harmless substances, called allergens, and release the same chemicals and proteins to fight off these allergens. Histamine, one of the immune response chemicals, leads to the symptoms of allergic reactions such as watery eyes, runny noses, wheezing, eczema, vomiting or diarrhea.
Cow's Milk Allergy
Milk allergy is the most common food allergy in toddlers, affecting more than 2.5 percent of children under age 3, according to the American Academy of Allergy Asthma & Immunology, or AAAAI. Milk-allergic toddlers may experience symptoms within minutes to hours after consuming milk or foods containing milk. There is evidence that some milk-allergic children may tolerate small amounts of milk in baked goods such as cakes, according to the AAAAI. Many toddlers will outgrow a milk allergy between ages 3 and 5.
Egg Allergy
Egg allergy is the second most common food allergy in young children, affecting about 2.5 percent of infants and young children. An allergy to eggs is hard to diagnose because eggs are a common but hidden ingredient in many foods, such as breads, pasta and salad dressings. Most toddlers will outgrow their egg allergies by age 5, reports the AAAAI.
Peanut Allergy
An allergy to peanuts is one of the most common causes of severe allergic reactions in children and adults, and toddlers are especially vulnerable because they cannot read food labels or learn to distinguish between peanut-free foods and allergenic foods. Around 80 percent of children with peanut allergies have their first exposure and reaction between the ages of 14 to 24 months, according to a July 2001 issue of the "Journal of Allergy and Clinical Immunology." Of these toddlers, only 20 percent will eventually lose their peanut allergies.
Animal Dander Allergy
Dander from pets such as cats and dogs are major causes of allergies and asthma in toddlers, explains a study published in the June 2004 issue of "Pediatric Allergy and Immunology." According to this study, toddlers who were living with cats in their first 2 years of life were more likely to have cat allergies and severe asthma at age 4. The study also found that asthma developed earlier and was more severe in toddlers who have asthmatic mothers and were exposed to cats when they were infants.
Dust Mite Allergy
House dust mites, or HDM, are microscopic ticks that live inside mattresses, pillows, furniture, carpeting and other warm, humid environments. HDM waste matter and dead mite particles, and not the mite itself, trigger the allergic reactions in toddlers sensitive to HDM. Toddlers who live in poorly ventilated homes have a higher risk of developing asthma and allergies from HDM, explains the "Pediatric Allergy and Immunology" study.
