Cow’s milk allergy (also known as cow’s milk protein allergy or CMPA) is an abnormal response by the body’s immune (defence) system in which proteins in a food (in this case cow’s milk) are recognised as a potential threat. This can cause the immune system to be ‘sensitised’. When this happens, there is the potential that when cow’s milk is consumed the immune system remembers this protein and may react to it by producing allergic symptoms.
Whilst cow’s milk allergy is one of the most common food allergies to affect babies and young children in the United Kingdom it is still rare. Formula fed babies, although very rarely, breastfed babies can also be affected. Allergic symptoms to CMPA can happen immediately after feeding or they can be delayed. In the case of immediate symptoms such as swelling of the lips or the tongue or breathing difficulties, immediate medical help must be sought.
There are two types of cow’s milk allergy depending on how the immune system reacts. Symptoms that are ‘immediate’ (quick to appear) are caused by the immunoglobulin E antibody (called IgE). Typically these allergic symptoms happen within minutes of consuming cow’s milk or up to two hours afterwards. This type of reaction is described as IgE mediated food allergy.
The other type of milk allergy happens when symptoms are ‘delayed’ (slow to appear) and are caused by a different part of the immune system reacting in a different way. This type of reaction is described as Non-IgE mediated food allergy and is the most common type. The symptoms typically develop from two hours after consumption but can take up to 72 hours. If cow’s milk continues to be consumed in the diet, the immune system will continue to produce such symptoms over days or even weeks.
Symptoms of CMPA often start in the early weeks and months of life. There are many possible symptoms which may suggest your baby has a cow’s milk allergy. Allergic symptoms can affect one or more of the body’s systems, including the skin, digestive and, less commonly, breathing or blood circulation. Allergic symptoms may be called mild, moderate or severe. However, it is important to note that some of these symptoms, such as reflux, colic and constipation are commonly seen in this young age group.
The immediate symptoms (see table below) occur quickly after consuming cow’s milk. They are most likely to be seen when weaning starts from breast feeding or when a change is made from breast feeding to formula feeding. The symptoms will usually be mild-to-moderate and often only affect your baby’s skin. It is very rare to see severe symptoms which can affect your baby’s breathing or how alert they appear. However, if you recognise such worrying severe symptoms, you should call an ambulance immediately as they could be potentially life threatening. This form of allergic reaction is called Anaphylaxis. Tell the emergency call handler that you suspect that it is an anaphylactic (pronounced ana-fi-lac-tic) reaction.
The delayed symptoms appear much more slowly and are also more likely to be mild-to-moderate. They are more difficult to relate to being caused by cow’s milk as they happen several hours after cow’s milk is consumed.
Key Message: Remember that many of the symptoms of delayed allergies, such as eczema, colic, reflux and diarrhoea are common in infants and milk allergy is only one of a number of possible causes. In most cases of cow’s milk allergy, your baby will show several symptoms in a pattern that will suggest either the delayed or immediate type of food allergy. Some of the symptoms can appear in both immediate and delayed allergic reactions. However, how quickly symptoms are seen usually gives the indication for the type of reaction.
Cow’s milk is made up of three main ingredients – protein, sugar, and fat. In cow’s milk allergy, it is the proteins called casein and whey that usually cause the problem. However, the sugar (lactose) in milk can also cause symptoms in some. This is referred to as Lactose Intolerance. It is important to understand the difference between lactose intolerance and cow’s milk allergy and to be aware that the management of lactose intolerance is very different from that of cow’s milk allergy. There are two types of lactose intolerance.
Primary Lactose Intolerance is the more common form and happens where there are reduced levels of the enzyme lactase in the digestive system. This enzyme is needed to break down lactose sugar found in milk, which the body can then absorb and use. As young children grow up and drink less milk, the amount of this enzyme gradually and naturally decreases. For some children, especially those from Asian or African ethnic backgrounds, this may mean that over time not all the lactose in the diet is broken down. Very gradually tummy symptoms begin to develop when lactose in milk is consumed. These symptoms may include bloating, tummy pains, wind and very loose poos (diarrhoea) – all of which can also be seen in milk allergy. However, this does not usually happen until later in childhood and is very unlikely to occur in young babies, which is the group most likely to show symptoms of cow’s milk allergy.
Secondary Lactose Intolerance occurs in some babies and older children who have been unwell with a gastroenteritis infection or who have been diagnosed with other digestive system related conditions such as coeliac disease. These conditions may cause temporary damage to the digestive system and reduce lactase enzyme levels, resulting in lactose intolerance symptoms. This is usually temporary and can be expected to resolve after a short period of time once the main cause has settled.
Key Message: The symptoms of both types of lactose intolerance can also be seen in milk allergy. This can lead to confusion with the mistaken conclusion that symptoms are due to lactose intolerance when the real reason is cow’s milk allergy.