Milk contains many protein fractions (allergens) that cause allergic reactions. The two main components are whey and casein, and an individual may be allergic to either or both. The casein is the curd that forms when milk is left to sour, and the whey is the watery fraction which is left after the curd is removed.
The whey fraction (20%) contains mainly alpha-lactalbumin and beta-lactaglobulin and is most likely to produce the IgE-antibodies (Immunoglobulin E) and causes the most clinical problems. These IgE-antibodies can be tested for in the blood, and by skin prick testing. The whey proteins are altered by high heat, and so the whey sensitive person maybe able to tolerate evaporated, boiled or sterilised (Long Life) milk and milk powder.
Casein (80%) is heat stable and is the most important allergen in cheese. The harder the cheese, the more casein is formed. This is the least allergenic for those individuals allergic to the whey fraction. Extensive heating may reduce only, but not eliminate, the allergenicity of the protein fractions.
There is cross-reactivity among milk proteins obtained from cows, goats and sheep. Only the whey fraction in the goat's milk differs from that in the cow's milk. Goat's milk is tolerated by only 40% of children who are allergic to cow's milk.
What is Milk Allergy/Intolerance?
Clinically abnormal reactions to cow's milk protein (CMP) may be due to the interaction between one or more milk proteins and one or more immune mechanisms. Reactions where the immune system is involved, which are mainly immediate IgE-mediated reactions (involving IgE-antibodies) are defined as cow's milk protein allergy (CMPA). Reactions not involving the immune system are defined as cow's milk protein intolerance (CMP).
Clinical Types of Milk Allergic Reactions
Reactions can be immediate or start several hours or even days after the intake of moderate to large amounts of CM.
Type 1 - Symptoms start within minutes of intake of small volumes of CM. Mainly causes skin problems, eczema or urticaria (hives). May have respiratory (runny nose, wheezy chest) or gastro-intestinal (vomiting and diarrhoea) symptoms.
Type 2 - Symptoms start several hours after intake of modest volumes of CM; mostly symptoms of vomiting and diarrhoea.
Type 3 - Symptoms develop after more than 20 hours, or even days after intake of large volumes of CM. Symptoms include diarrhoea, with or without respiratory or skin reactions.
TABLE 1. Symptoms that could indicate a possible milk allergy
TABLE 2. Label Ingredients that may contain milk protein
How is Milk Allergy Diagnosed?
Only the immediate milk reactions that develop after a few minutes are most likely to give a positive blood or skin test, as these detect IgE that is involved in the immediate type reaction. Nearly 60% of milk reactions in the young child are the delayed type (intolerant) and therefore unlikely to give positive results with the blood and skin tests. The diagnosis is then made by the Elimination-Challenge Test. This should demonstrate the relief of symptoms on the removal of milk from the diet and the recurrence of symptoms when re-introduced. This Elimination-Challenge Test should be supervised by the doctor and the dietitian.
Skin Prick Tests
SPT can be used, and are especially accurate in the young child. Small drops of the suspected milk or other foods are placed on the forearm. A small prick is made through the drop into the skin. A wheal and flare reaction after 15 minutes will indicate that the patient is allergic to the milk.
Blood Tests ("CAP RAST")
A small blood sample is taken by the nurse or the doctor and sent to the laboratory for testing. This CAP RAST tests for milk protein as a whole or the individual fractions of milk. Available CAP RAST tests are:
Cheese - cheddar type
Cheese - mould type|
The CAP RAST and the skin prick tests are reimbursed by Medical Aid.
Guidelines for Nutritional Management
No milk-free diet should be undertaken without the supervision of a dietitian, who will provide milk-free recipes and a list of alternative products to ensure a nutritionally adequate diet, in order to avoid a deficiency of calcium, riboflavin and vitamin D.
All pregnant and breast-feeding mothers, children and adults on a dairy-free diet, must have their calcium replaced, otherwise this could lead to dental and bone problems. The correct dosage and type of calcium supplement is to be advised by the doctor and dietitian.
Milk may be present where you least expect it. For example in viennas, sausages, fish fingers, pie crusts, biscuits like Provita and breakfast cereals.
Milk substitutes in the form of soya or hypo-allergenic whey and casein formulas may be given to the young infant on the advice of the doctor. Unfortunately they are extremely expensive. 25% of milk-allergic infants may become allergic to the soya protein. What then is the alternative? Home-made meat-based formula (e.g. lamb, chicken, turkey) may be advised by the dietitian.
Will my child outgrow the milk allergy?
Most children will outgrow their CMA, +60% at 4 years and +80% at 6 years. Some patients retain the allergy throughout life. If the milk is strictly excluded from the diet for + 2-3 years, the child then has an 80% chance of tolerating the milk in small amounts again. CMA may be acquired later in life.