The numbers are striking: 20 to 40 percent of children in the United States have at least one allergy, according a report from the World Allergy Organization.  At a time when so many kids are suffering, parents and researchers alike are looking for answers. How do allergies and asthma get their start? Is there really any way to keep them from happening? How to allergy-proof your homeMost allergies develop during the first year or two of life. And if you or your partner has allergies, your baby is more likely to develop allergies too. But if you can keep her away from the most highly allergenic substances while her immune system has a chance to mature, you just might help her avoid allergies entirely.Feeding your infant nothing but breast milk for the first six months of life is the most effective weapon against allergies. For one thing, breast milk promotes a healthy immune system. And unlike cow's milk or many types of formula, breast milk doesn't contain proteins that can easily trigger an allergic reaction.