Milk proteins and lactose

Allergy to milk is a reaction to the proteins in contrast to lactose intolerance, where the milk sugar, i.e. lactose is causing the problems. Individuals with milk protein allergy must avoid all milk products including cheese. Individuals with lactose intolerance tolerate cheese and small amounts of milk products.

Allergy to milk proteins

Milk protein allergy is a serious condition. The symptoms of an allergic reaction can vary from mild to severe, from eczema, vomiting and stomach pain, to asthma and systemic anaphylactic shock. Under special circumstances, death has occurred to milk. Even tiny amounts of milk/milk proteins can elicit severe allergic reactions in sensitized individuals.

Lactose intolerance

Lactose (milk sugar) is a natural component in all kinds of milk. Lactose intolerant individuals have reduced levels of an enzyme, lactase, needed to hydrolyze lactose in the small intestine. Lactase deficiency allows the lactose to reach the large intestine where it is fermented by the micro flora in the colon.

Symptoms of lactase deficiency are stomach/intestinal distension accompanied with pain, flatulence and diarrhea. The individual sensitivity to lactose varies but most individuals tolerate small amounts of lactose, corresponding to approximately 100 ml of milk per day.

Milk - a very common ingredient

Milk is a common ingredient in several different kinds of food like ready to eat dishes including sausages and meatballs, cakes, cookies, bread etc. Dark chocolate is often contaminated with milk and the concentrations can be very high. Concentrations above 1000 mg casein/kg chocolate were found in the Nordic control project – Undeclared allergens.


The presence of milk and products thereof including lactose in food products must always be declared, see further in the Food Information Regulation (EC) no 1169/2011.

Examples of methods of analysis

Cow's milk contains a number of different proteins. Caseins and the whey proteins lactoglobulin and lactalbumin are present in highest concentrations. Allergic individuals may react to one or several of these milk proteins. In addition, other proteins in cow's milk have been associated with allergic reactions. The caseins are the dominating proteins in milk and constitute about 80 percent of the proteins. The caseins are heat stable and thus suitable for the analysis of milk/milk proteins in food. The whey proteins are the residual proteins in milk after removal of the caseins, i.e. about 20 percent of the proteins in milk.

Lactoglobulin is one of the proteins in the whey fraction. Lactoglobulin is not as heat stable as the caseins but can be used as a complement for the analysis of milk in food products. The caseins are a better indicator for the presence of milk/milk proteins in compound food products unless only the whey fraction was included in the product to be analyzed.

Sensitive commercial ELISA test kits are available for the analysis of casein or lactoglobulin. The limit of quantification varies somewhat between different test kits and depends also upon the matrix. The limit of quantification for casein is as low as 0.5 mg/kg in certain matrixes.

Lactose can be quantified with an enzymatic method (lactose/galactose). The limit of quantification is just below 100 mg/kg. The enzymatic method is not suitable for the analysis of products where lactase has been added for the hydrolysis of lactose. Such products can be analyzed with chromatographic methods like HPLC or GC.

Accredited methods should be used in official control. The Swedish Food Agency is accredited for analysis of casein in food.

Allergic reactions / Doses

The lowest dose of milk proteins/caseins that elicits an allergic reaction is not known. However, individual oral food challenge data can be compiled in order to estimate the proportion of the allergic population that would be likely to react to a certain dose of an allergen. The Swedish Food Agency has used such published data and developed a guide on how to calculate the risk of allergic reactions to certain concentrations of e.g. milk. The guide is in English and can be reached below (L 2022 nr 13).

The Swedish Food Agency has analysed concentrations of milk protein in food that have caused unexpected allergic reactions. The food and the descriptions of the allergic reactions have been sent to the Swedish Food Agency by the health care or by control authorities. A proportion of these reactions is presented in the table below. The presented examples are chosen in order to show that unexpected allergic reactions to milk protein can occur to different doses of milk, be caused by different food categories and cause different symptoms. The amount of food that has been consumed is estimated in most cases and the dose is thus partly estimated. Caseins constitute about 80 % of the total milk proteins.

Food  Consumed amount Casein conc. mg/kg Estimated dose   Symptoms  Age (years)
Cinnamon bun 15 g 4 0.06 mg Stomach pain 3
Pasta with tomato
200 g 0.8 0.16 mg Anaphylactic shock* 3
Bun 60 g 4.5 0.27 mg Nausea, itching 7
Noodles 30 g 12 0.36 mg Stomach pain, itching of the oral mucosa 14
Lasagna 50 g 7.5 0.38 mg Anaphylactic shock* (asthma, itching) 14
Candies 30 g 30  0.9 mg Anaphylactic reaction*  6
Chips 15 g 8 1.3 mg Itching of the oral mucosa, swelling
of the lips
Soy-based yoghurt 20 ml 107 2.1 mg Anaphylactic shock* 8
Chocolate cake 10 g 250 2.5 mg Anaphylactic shock*, (asthma, stomach pain, itching) 10
(non-milk based)
15 g 18 2.7 mg Stomach pain, swelling of the
lips and throat
Biscuit 25 g 300  7.5 mg Vomiting,
Chocolate cake 5 g 1200 6.6 mg Anaphylactic shock* 9
Soy-based formula 250 ml 40 10 mg Asthma,
Soy-based ”cheese” 20 g 580 12 mg Anaphylactic shock* 20
Chocolate 10 g 1300 13 mg Itching 1
Meat balls 20 g 890 17 mg Stomach pain, itching and
swelling of the
lips and throat
Chocolate 22 1000 22 mg Anaphylactic shock* 62
Chips 40 g 830  36 mg Fatal
Gravy 4 g 8900 36 mg Urticaria,
swelling of
the lips
Fish soup 50 g 1000 50 mg Anaphylactic shock* 4
Sausage 100 g 600 60 mg Fatal
Coleslaw 40 g 2240  90 mg Anaphylactic shock* -
Pancake 50 g 4300 215 mg Itchy throat


Meal replace-ment 35 g 8900 310 mg Anaphylactic shock*


* Anaphylactic shock means that the allergic individual suffers from a severe allergic reaction that induces symptoms from several organs. At least one of the symptoms has to come from the airways, the circulation or the general condition needs to be severely affected in order for the reaction to be classified as an anaphylactic shock (The Swedish Association for Allergology).

** Fatal anaphylaxis means that the shock proceeds to unconsciousness and death

Reviewed 2023-11-01