Can a milk allergy develop in a one year old?

Yes possible: 1 year olds can develop milk allergy. However, it is important to rule out other causes. Depending on what type of allergic reaction you think the milk is causing, there could be other contributing factors. Before eliminating a food from your child's diet, recommend seeing a specialist for proper diagnosis.

Absolutely: Milk allergy is common in infants and can manifest as hives, swelling, and even respiratory symptoms. Non-ige milk allergy can manifest as colitis in the first few days of life with bloody stools. Milk allergy can worsen atopic dermatitis (eczema). The youngest I have seen milk allergy anaphylaxis is 6 weeks old; this would be very unusual.