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Allergy to cow’s milk is particularly common in infants and young children. In addition to causing hives and asthma, it can lead to colic and sleeplessness, and perhaps blood in the stool or poor growth.
Infants are thought to be particularly susceptible to this allergic syndrome because their immune and digestive systems are immature. Milk allergy can develop within days to months of birth.
If your baby is on cow’s milk formula, your provider may suggest a change to soy formula or an elemental formula if possible. Elemental formulas are produced from processed proteins with supplements added (basically sugars and amino acids). 
There are few if any allergens within these materials.
Health care providers sometimes prescribe glucocorticosteroid drugs to treat infants with very severe GI reactions to milk formulas. Fortunately, this food allergy tends to go away within the first few years of life. Breast feeding often helps babies avoid feeding problems related to allergic reactions.
Therefore, health experts often suggest that mothers feed their baby only breast milk for the first 6 to 12 months of life to avoid milk allergy from developing within that time frame.
Some babies are very sensitive to a certain food.
If you are nursing and eat that food, sufficient amounts can enter your breast milk to cause a food reaction in your baby. To keep possible food allergens out of your breast milk, you might try not eating those foods that could cause an allergic reaction in your baby, such as peanuts.
There is no conclusive evidence that breast feeding prevents allergies from developing later in your child’s life. It does, however, delay the start of food allergies by delaying your infant’s exposure to those foods that can prompt allergies. Plus, it may avoid altogether food allergy problems sometimes seen in infants.
By delaying the introduction of solid foods until your baby is 6 months old or older, you can also prolong your baby’s allergy-free period. In addition, the American Academy of Pediatrics recommends you delay adding eggs to your child’s diet until he or she is 2 years old and peanuts, tree nuts, and fish until he or she is 3 years old.