An allergy is an adverse immune response to substances by smell, physical contact, or ingestion. The reaction time can be between two and 24 hours after contact with the allergen. Unlike food intolerances, it is rare for allergies to disappear over time.

One kind of food allergy one can have is milk. The milk proteins, which are benign to non-allergic individuals, trigger immune reactions that vary in intensity in those allergic. Individuals can be allergic to one or both of the milk proteins (casein and whey). The intensity may vary depending on the animal source of the milk. Based on the reaction time and intensity, a milk allergy is clinically classified into three types:

• Type 1 milk allergy: This form of allergy occurs in response to a small quantity of milk within a short duration. It is manifested by skin issues, such as eczema and hives, respiratory problems, such as sneezing and a runny nose, and gastrointestinal problems such as nausea, vomiting, and diarrhea.
  
• Type 2 milk allergy: This form is characterized by gastrointestinal symptoms (e.g. vomiting and diarrhea) within a few hours post consumption.
  
• Type 3 milk allergy: This type of milk allergy response occurs when large quantities of milk are consumed. The reaction may show up after nearly a whole day or even after a few days and can lead to clinical signs of skin, respiratory, and gastrointestinal tract problems, similar to that of a type 1 milk allergy.
  

Other symptoms of a milk allergy include bloody stools and in rare cases, may cause anaphylaxis, a breathing impairment that can set the body into a shock state and can be fatal.

Milk is one of the top ten food allergens. Thus, it is important to observe any allergic responses and have it diagnosed immediately with a food allergy test. These tests help confirm if the issue is an intolerance or an allergy.  Another way to test if it is a milk allergy or intolerance would be to introduce small quantities of different forms of milk or milk products and gradually increase the quantity. If none of the three milk allergies manifest themselves, then it suggests milk intolerance, not an allergy. However, the best way to confirm if it is an intolerance or an allergy is to get a food allergy test. The best way to combat a milk allergy is to avoid it completely.

References:

Motala, C. Food Allergy. Retrieved from http://www.worldallergy.org/public/allergic_diseases_center/foodallergy/

Sachan, N. & Singh, V.P. (2011) Milk Allergy: An Overview. International Journal for Agro Veterinary and Medical Sciences, 5 (3), 368-376. Retrieved from http://www.scopemed.org/?mno=5634#references

Milk & Dairy Allergy. Retrieved from http://acaai.org/allergies/types/food-allergies/types-food-allergy/milk-dairy-allergy

Milk Allergy. Retrieved from http://www.allergyuk.org/milk-allergy/milk-allergy

(2011 Dec 6). Milk Powder Better than Liquid Drops to Treat Milk Allergies. Retrieved from http://www.hopkinschildrens.org/Milk-Powder-Better-than-Liquid-Drops-to-Treat-Milk-Allergies.aspx