Allergens are things which trigger allergies in people.
Because babies are very sensitive to developing allergies in the first two years of life, it's important to help them avoid these allergens as much as possible. Like other common allergens such as grasses and preservatives found in some foods, they cause some people to react in a certain way. Some people react by sneezing or having a runny nose or eyes. People with asthma react by wheezing or having difficulty breathing. Although there are millions of these creatures in our houses, they are too small to see.