Exclusively breastfeeding your baby is recommended by the WHO for at least the first 6 months of life. Often described as ‘breast is best’, it is well known across the world that breast milk and breastfeeding are beneficial to both mother and baby. Your breast milk contains all of the nutrients that your baby requires to thrive in its first few months of life. However, what happens if it appears that your breast milk is making your baby unwell or unhappy?

In a very small percentage of babies, ‘food allergens’ which can exist in microscopic quantities in breastmilk, can cause a baby to have an igE or non-igE mediated allergic reaction.¹² Once it has been established that a baby is having a reaction to a food allergen transmitted through the breast milk, then it is important to determine which food product is causing it so that the mother can eliminate the offending allergen from her diet.

Read on to understand which foods most commonly cause an allergic reaction, how they get to your breastfed baby and what the symptoms of an allergic reaction may look like in your baby.

What is a food allergy?

A food allergy is an abnormal reaction of the immune system that is triggered by ingesting a food protein antigen.³ The body recognises the food protein as a ‘foreign invader’ and launches an immune response which can cause a variety of symptoms. An allergic reaction to a food product can be IgE-mediated, non-IgE-mediated or mixed. An IgE-mediated response typically occurs within minutes to hours after the offending food has been eaten whereas a non-IgE-mediated response is delayed and can occur up to 48 hours later. A non-IgE mediated response still involves the immune system however it is often less severe and there is a wide spectrum of symptoms, commonly involving the skin and the gut and it is often wrongly mislabelled as an ‘intolerance’ instead of an allergy.⁴ 

Allergy vs. intolerance

Food allergies and intolerances, particularly in babies, can be difficult to distinguish between. An allergic reaction to a food protein always involves an immune system response and can either be IgE-mediated, non-IgE-mediated or mixed. The most severe form of an allergic reaction is called anaphylaxis, which is a life-threatening IgE-mediated reaction requiring prompt medical treatment. However, not all allergic reactions to foods cause anaphylaxis. Many, especially non-IgE mediated allergies, present far more insidiously making them much harder to accurately diagnose and are often misdiagnosed as an intolerance.⁴ Intolerances to certain foods, for example, gluten, dairy or lactose, do not involve the immune system. The symptoms however can appear very similar to those of a ‘mild or moderate’ food allergy often involving the gut and the skin. To distinguish between the two, a doctor will likely need to take a full history including a food history from the mother and may suggest further tests such as undertaking diet elimination, blood tests to look for an immune response, or skin prick testing to look for a reaction.

How does an allergen reach a breastfed baby?

You may be wondering how an exclusively breastfed baby is exposed to a food allergen if the only thing they are consuming is breast milk. Recent research has shown us that minuscule food particles absorbed by the gut in the mother can be transferred via breast milk to their baby. The amount of allergen that is transmitted varies from mother to mother and feed to feed. Some mothers don't transfer any food particles even if they have just eaten. Even when an allergen is transferred in breast milk it is highly processed and in tiny amounts and tolerated by the vast majority of babies. However, occasionally a baby can develop an allergy to food proteins transferred in breast milk.⁵

Should you avoid any foods whilst breastfeeding? 

Exclusive breastfeeding has been proven to be the optimal source of nutrition for a baby in the first few months of life.⁶  To breastfeed successfully, a mother needs a balanced diet. She should avoid certain foods, like dairy products, as they may affect the infant. There's no evidence to support that consuming dairy is good for either the mother or child during breastfeeding.¹ In fact, in recent years the evidence has even started to point the other way. Breastfeeding is now considered to be a protective factor against infants and children developing food allergies.⁷ The countries such as the USA and the UK have changed in recent years from avoiding potential allergens until children are older to introducing them during weaning from age 4-6 months. Even when a child is considered more at risk of developing a food allergy it is still not recommended for the mother to avoid any food groups.⁸

Common allergens in the breastfeeding diet

As we have seen, there are different types of allergic reactions that can occur in reaction to food particles. The most severe of these are IgE-mediated reactions, which can induce anaphylaxis. An IgE-mediated reaction in an exclusively breastfed baby is incredibly rare. It is more likely to occur through sources outside of breastfeeding, such as during weaning or through the introduction of supplementary formula feeds. In exclusively breastfed infants, the most common allergic reaction is a non-IgE-mediated reaction due to cow’s milk protein allergy. Although still involving the immune system, these reactions are delayed, occurring hours to days after the offending agent has been consumed in the breast milk, which in turn can be hours after the mother herself consumed the food. There are five different types of non IgE-mediated reactions and we will discuss their differences below.⁵

A list of the most common allergens:

• Cow's milk protein allergy (the most common allergy in babies)
• Eggs
• Peanuts
• Tree nuts
• Soy
• Wheat
• Fish
• Shellfish

Allergic reactions in breastfed babies

Symptoms of food protein-induced allergic reactions in infants

IgE-mediated reactions 

These are often the most severe allergic reactions and can induce anaphylaxis. For unknown reasons, cow’s milk, peanuts, and eggs are the most likely foods to cause this type of reaction. Symptoms in infants may present differently from  a ‘typical’ severe allergic reaction and include the following:⁴

• Urticaria (hives)
• Lethargy (floppiness)
• Vomiting
• Respiratory symptoms: wheeze, cough, swelling of lips, cyanosis
• Non-specific symptoms: loose stools, irritability, hoarseness

Non IgE-mediated reactions

These reactions can occur hours to days after the infant has consumed the offending food protein transmitted through the breast milk. The most common cause of these reactions is cow's milk and soya. They tend to be less acutely severe but can cause a number of different symptoms predominantly involving the gut and skin:⁵

• Protein-induced allergic proctitis – typically presents between 2-8 weeks of age. Presents with fresh blood-streaked, mucousy, loose stools in infants who are otherwise well and thriving.  Caused by an allergy to cow's milk and in most infants the symptoms resolve after the mother eliminates cow's milk from her diet. Most infants will outgrow this allergy by age 1
• Dietary protein enteropathy – leads to the destruction of the gut lining which causes poor absorption and ‘failure to thrive’. Symptoms include chronic diarrhoea, vomiting, bloating and a generally ‘colicky’ unhappy baby
• Food protein-induced enterocolitis syndrome – this is a potentially severe reaction that occurs 1-3 hours after consuming the allergen. It can cause severe vomiting which can lead to dehydration and shock. Diarrohea can also occur 5-10 hours later. It is extremely rare in exclusively breastfed infants but can occur due to cow’s milk or soy
• Allergic eosinophilic oesophagitis  – this causes chronic inflammation of the oesophagus (food pipe). The most common allergen is cow’s milk. This inflammation can cause symptoms of reflux, vomiting, difficulty swallowing, irritability and feeding difficulties. It is commonly mistaken for reflux however does not resolve with typical reflux treatment.
• Motility disturbances – this occurs when an allergic reaction disturbs gut motility leading to a presentation of vomiting, reflux, constipation or colic

Diagnosing food allergies in breastfed babies

The successful diagnosis of a food allergy in an exclusively breastfed baby can be a difficult process to achieve. For starters, genuine allergic reactions to food proteins transmitted in breast milk are rare. More commonly infants suffer from intolerances such as lactose intolerance, colic, reflux, eczema or other medical issues which have overlapping symptoms with those of a food allergy. However if your doctor is concerned your baby may be suffering from an allergy, they may do some or all of the following:⁵

• Detailed history including the food history of the mother and her genetic history
• A full examination of the baby
• Skin prick testing - this can be momentarily uncomfortable for your baby but is a good diagnostic tool when looking for which allergen may be causing your baby a reaction
• Blood tests -these can show when there is an IgE-mediated reaction and sometimes will tell you which allergen is causing it
• Food challenge - if other results are still unequivocal, then a food challenge can be done to elicit a reaction. However, this will not be done on babies who present with signs of a severe or anaphylactic reaction
• Elimination and reintroduction diet - for non-IgE-mediated allergic reactions, a diagnosis can not be achieved via blood tests or skin prick testing. Typically a diagnosis will require an elimination diet followed by reintroduction. If symptoms resolve during the time, the mother has eliminated the potential allergen from her diet and restarted when reintroduced then this is diagnostic of an allergy

Management of food allergies in breastfed babies

The predominant management of an infant who has been diagnosed with a food allergy, and is displaying symptoms is the elimination of the offending food from the maternal diet. If this is not sustainable or possible, then the addition of an appropriate feeding supplement should also be considered. Infants who are diagnosed with an IgE-mediated allergy will also need an anaphylaxis plan as well as being prescribed an epi-pen (Adrenalin) for emergencies.⁶ 

Weaning

Weaning typically starts from 4-6 months of age. When weaning a baby with known food allergies particularly those with IgE-mediated reactions, then the infant must avoid the offending food unless instructed to re-introduce it under the supervision of their clinician. For non-IgE mediated allergies, the breastfeeding mother may be invited to reintroduce the offending allergen whilst still breastfeeding. However, any introduction of a known allergen to a baby or child should only be done under strict instructions from their healthcare provider.⁶

Emergencies

If your baby is displaying signs of a severe (IgE-mediated) allergic reaction then seek medical advice urgently. Anaphylaxis can occur at any point and requires emergency medical care. Symptoms of  severe allergic reactions include but are not limited to:⁶

• Urticaria (hives)
• Angioedema (swelling of lips, tongue, face)
• Vomiting
• Cough or wheeze
• Cyanosis (turning blue or blue-tinted lips)
• Lethargy (floppiness)

Strategies to avoid common allergens

• Reading food labels
• Dietary substitutions for allergenic foods
• Identifying hidden sources of allergens - make sure you’re aware of all the different names that an allergen can be referred to. For example, dairy can be referred to in many different ways on an ingredients list

Summary

• Although rare, an exclusively breastfed baby can have an allergic reaction to food products.
• Food proteins are found in minuscule amounts within breast milk and can be transmitted to a baby through breastfeeding. It is unclear why the amounts found in breast milk vary from woman to woman and feed to feed.
• The most common allergen found to affect breastfed babies is cow's milk protein.
• Symptoms can range from those of anaphylaxis to more chronic symptoms involving the gut or skin.
• It is not recommended for breastfeeding women to eliminate food groups from their diet without any evidence that their infant is suffering from an allergic reaction. There is evidence to suggest that breastfeeding can protect a baby against developing future food allergies.
• There are two types of allergic reactions that can occur, IgE mediated reaction which tends to be more severe and can induce anaphylaxis, although is extremely rare and a non-IgE mediated reaction. Both involve the immune system.
• Management of a food allergy in an exclusively breastfed infant involves the elimination of that food group from the mother's diet.