Reactions to milk vary in their underlying cause. They also vary in their symptoms and presentation: hives and wheezing after drinking milk; difficult-to-control eczema that improves with milk elimination; blood in the stool in an 8 week old infant; projectile vomiting in a formula-fed infant; bloating and abdominal cramping after eating dairy products.
In the truest sense of the word, "allergy" to milk refers to an immediate and reproducible reaction to milk protein that triggers a characteristic reaction caused by the release of histamine and other chemical mediators and cells in the skin, gut, and respiratory system. Typical symptoms begin within 5-20 minutes after ingestion and resolve within hours. Symptoms and signs include hives in 80-90% of cases, and, less commonly, vomiting and abdominal pain, itchy and watery eyes and nose, coughing and/or wheezing, and sometimes a fall in blood pressure.
Milk allergy is diagnosed by skin prick or blood tests. Most children outgrow milk allergy in middle childhood, but up to 20% still have the allergy into adolescence and adulthood. Up to a third of children with eczema have a food allergy, most often to milk, egg, or peanut.
Reactions to milk that have a rapid onset, or are severe or progressive must be treated with self-injectable epinephrine (the "Epi Pen"). Patients and families that have these types of reactions should have an action plan to deal with them.
The only current long-term treatment for milk allergy is strict avoidance of all dairy products. However, there is some recent data that suggests that regular ingestion of baked milk (in muffins, for example) may help accelerate the development of tolerance. Unfortunately, up to 30% of milk-allergic children do not tolerate baked milk, so this eating regimen should only be undertaken after a discussion with an allergist. For children < 2 years of age, during this time of rapid growth and development, attention must be paid to fat and protein content of milk-substitutes. It should be noted that rice or soy milk do not contain comparable fat and protein to the more nutritional toddler soy or hypoallergenic formulas.