If my baby is allergic, will I know right away?

Probably not. It can take time for an allergy to develop. Each allergic person has a threshold that must be met before an allergen causes a reaction, and this can take several months.

So if your baby inherited the tendency to be allergic to cat dander, she may have no trouble at all for the first few months she's around Fluffy, or she may have a reduced reaction. But then one day, when the exposure level reaches her threshold, her body will react and mount an offense.

Seasonal allergies to things such as pollen and grass usually don't rear their ugly (and stuffy) head until a child is about 3 to 4 years old.