Why the fuss about milk?
Milk allergy is one of the common food allergies among young children and can cause considerable parental concern.
It has a somewhat mercurial reputation, perhaps because there are two types of milk allergy with startlingly different implications. ‘Immediate’ milk allergy is mediated by IgE antibodies which carries a risk of anaphylaxis and so emergency medication may be appropriate. The non-IgE (‘delayed’) milk allergy has no diagnostic test, causes a concern among parents and attracts media attention.
Many aspects of confusion can be cleared up through outlining some principles here, whilst tailoring management towards a particular child requires talking through any allergy symptoms in more detail.
What are the stats?
Cow’s milk allergy affects around 2.4% of UK infants with 0.5% having immediate IgE-mediated milk allergy and around 1.7% having non-IgE milk allergy according to the recent Hampshire birth cohort. The good news is that the majority of young children grow out of their milk allergy – and commonly by 2 years of age. However, it can present with symptoms that are very common in early childhood and therefore many parents worry that cow’s milk protein ingestion may be causing trouble when it is not necessarily the cause.
What foods contain cow’s milk protein?
Foods containing cow’s milk protein include fresh cow’s milk, dairy products (including yoghurt, butter, cheese and cream [not egg]) and also ‘baked milk’ products that use milk products as an ingredient. Other animal milk proteins, such as goat, sheep and buffalo, are very similar to cow’s milk and often also cause symptoms for those allergic to milk. Therefore, switching to goat’s milk etc. is very unlikely to be helpful for a person with an allergy to cow’s milk.
What are the signs of an ‘immediate’ cow’s milk allergy?
Children who are allergic to cow’s milk have immune systems that recognise binding sites within the proteins of cow’s milk.
In the case of immediate IgE-mediated milk allergy, the immune system makes ‘IgE’ antibodies that bind to specific epitopes (protein recognition regions) within the cow’s milk protein and trigger an immediate reaction. IgE-mediated reactions usually develop within 15 minutes of ingestion (see Box 2). Common immediate reaction symptoms include a bumpy raised itchy rash called urticaria (like nettle rash) with lip, eyelid or skin swelling, and vomiting.
More serious immediate symptoms – such as throat closing, noisy or difficult breathing and drowsiness – require an ambulance and intramuscular injection with adrenaline if available.
What signs may indicate a ‘delayed’ non-IgE cow’s milk response?
Unfortunately, many troubles related to non-IgE cow’s milk allergy are very common among young children anyway even when entirely unrelated to ingestion of cow’s milk protein and therefore not an allergy. Since there are no accurate proven diagnostic tests available for non-IgE milk allergy, we have to rely on careful history-taking to see whether an exclusion diet should be considered as part of diagnosis. Symptoms of ‘delayed’ cow’s milk allergy (previously called intolerance) can develop over a longer period of time and can take weeks to improve after avoidance.
Delayed milk allergy symptoms can include reflux with vomiting, food aversion, abdominal pain, constipation, diarrhoea and difficult eczema flares. More serious symptoms may also present, such as passing mucus and blood in the stool, food getting stuck in the oesophagus when swallowing, and not gaining weight. These symptoms require a prompt medical evaluation.
If the only symptom of concern is eczema flaring without gastrointestinal signs, the eczema must be treated with an appropriate strength of topical steroid ointment for a period specified by your doctor, before considering whether cow’s milk ingestion may be contributing to disease. Where eczema does not respond to an adequate strength of topical steroid therapy and may be linked to increasing milk in the diet, a detailed history should be discussed with a doctor or dietitian who has established expertise in allergy, before any dietary exclusion is considered. Also bear in mind that there can be many triggers for eczema so it may not be milk or milk alone that is causing troublesome eczema.
What is not cow’s milk allergy?
The majority of symptoms associated with milk allergy can be caused by something else. Therefore, parents often show concerns of cow’s milk allergy when other treatments and management are more likely to bring relief. Reflux, wind, constipation, nettle rash, diarrhoea and eczema are very common among babies and often have no link to cow’s milk ingestion. This is why many services prefer to assume that the individual symptoms should be routinely treated separately before considering cow’s milk allergy. However, if delayed milk allergy symptoms present at the time of increasing milk ingestion in a reproducible fashion, it is important to seek medical help and ask directly about milk allergy rather than initiating dietary avoidance without any supportive medical advice. For instance, children who have to avoid cow’s milk protein in view of their allergy have significantly impaired growth.
Symptoms of lactose intolerance are caused by the sugar in milk (called lactose) and is therefore not an allergy and is never dangerous. Lactose intolerance causes bloating, discomfort and diarrhoea. People recovering from gastroenteritis or of Asian ethnicity can have low levels of lactase (which digests the lactose sugar), resulting in symptoms. Lactose intolerance symptoms may be relieved by switching to lactose-free milk and lactose-free dairy products. However, skin rashes, skin swelling, eczema, mucus or blood in the stool suggest other causes, and lactose-free products will not help.
How do we know if milk allergy is IgE-mediated or non-IgE ‘delayed’?
Rashes, vomiting, abdominal pain and diarrhoea may be caused by both immediate and delayed milk allergy. In these unclear cases, we use skin-prick testing and IgE antibody blood testing to look for the antibodies associated with immediate milk allergy. We never use IgG antibody testing, because it has no use in diagnosing food allergy.
Skin-prick testing allows us to test for food specific IgE antibody before you leave your appointment. We place a drop of milk (for example) on the forearm and prick the skin under the droplet with a lancet. This introduces a tiny amount of allergen under the skin surface, and we measure the diameter of the small white raised swelling (called a weal) around 15 minutes afterwards. The patient’s history and size of wheal help determine whether immediate milk allergy is likely.
There is no similar quick test for delayed milk allergy. Therefore, we assess for delayed milk allergy responses by avoiding all dairy (milk and milk products) for 4–6 weeks and then reintroducing it into the diet to see if the symptoms recur. It is important to discuss this with your doctor before undertaking milk avoidance diets. An experienced professional may be able to determine delayed milk allergy from your history alone and recommend appropriate action. Professional advice is important because avoiding milk can reduce energy, protein and calcium intake. In addition, at least one-half of patients with delayed milk allergy will also develop symptoms with soya ingestion. Therefore, undertaking safe and rigorous avoidance of both milk and soya requires planning what alternatives are best in close consultation with a qualified dietitian.
Planning milk avoidance and choosing alternatives
It is very important to manage milk allergy alongside advice from a qualified health professional (nurse, dietitian or doctor) to ensure safety and discuss nutritional replacement foods. The health professional may recommend that it is safe to continue with cooked foods that contain milk powder or baked dairy products if symptoms are negligible or absent when they are eaten. However, there is little good-quality evidence that regularly eating products containing processed milk will speed up the development of milk tolerance, although they can improve quality of life.
For babies and young children who are breast/formula-fed, a management plan becomes even more important to ensure adequate growth. A professional may discuss whether a woman breastfeeding needs to remove dairy from her diet or not, if continuing breast feeding. If formula is required, appropriate advice can be given on whether an extensively hydrolysed formula (EHF) or amino-acid-based formula is necessary. Techniques to establish these in the infant’s or child’s diet can be discussed. Whilst there are a number of alternative milks derived from other foods available for those with cow’s milk allergy, it is important to ensure that their nutritional composition is adequate for growth and health. Soya is not recommended for infants under 6 months of age due to phyto-oestrogens and must be fortified with calcium (rendering ‘organic soya milk’ unsuitable). Oat milk is commonly used as a milk substitute because it has a higher protein concentration than seed, coconut and tree nut milks. Rice milk is rarely considered a suitable substitute because it may contain inorganic arsenic, has little nutritional value and should only be considered an option after discussion with an experienced professional. Alternatives to milk formulae should be assessed at least yearly. For older children, the more nutritious milk alternatives include oat milk and soya milk.
Managing cow’s milk allergy safely
For immediate milk allergy, it is important to consider whether carrying an adrenaline auto-injector is warranted.
Your health professional will consider this and ask if cow’s milk ingestion has caused breathing difficulties or drowsiness, or if there is any asthma, before discussing whether to recommend adrenaline. Families receiving a prescription for adrenaline should be trained in how to use the device with a dummy trainer device and be given an emergency reaction plan so that they know which symptoms require early treatment with adrenaline.
There are some studies assessing whether milk immunotherapy can be used to treat milk allergy and this is an area of growing interest. Any interested families should discuss with expert clinicians to assess whether this may be appropriate before considering whether this may be a helpful choice for their child.
The Anaphylaxis Campaign – www.anaphylaxis.org
Allergy UK – www.allergyuk.org
The British Dietetic Association – www.bda.uk.com – and their milk allergy guidance
I would like to acknowledge helpful comments from Ruth Chalmers, registered dietitian at Children’s Allergies Department, St Thomas’ Hospital, London.