Cow’s Milk Allergy vs lactose intolerance

Food intolerance and allergy are both examples of ‘food hypersensitivity’ but the mechanisms by which they occur are very different.¹

• This occurs when the body’s immune system reacts inappropriately to the proteins in food.¹
• Broadly classified into those that are IgE mediated (immediate reaction), and those that are non-IgE mediated (delayed reaction).¹

• Does not involve food proteins and is a non-immune mediated reaction.
• Can be caused by either an absence of an enzyme needed to fully digest a food or a pharmacological reaction where the body reacts to certain naturally occurring substances in foods such as vasoactive amines, salicylates, caffeine and alcohol.

Lactose intolerance is where there is reduced capacity to digest lactose, a sugar naturally found in all mammalian milk due to an absence or deficiency of the enzyme lactase in the small intestine.¹

Malabsorption, therefore, occurs when lactose passes through the intestines without being absorbed, acting as a bacterial substrate in the colon which fuels gastrointestinal symptoms such as:

• Diarrhoea
• Flatulence
• Nausea
• Gut distension
• Abdominal pain

The degree of gastrointestinal symptoms is dependent on the amount of lactose ingested and levels of lactase present in the small intestine.^2-4

• This is extremely rare, presenting typically in isolated population groups such as Finn’s and Russians² and is evident from birth.

• Associated with the natural decline of lactase enzyme levels. It typically occurs around 3 years of age although symptoms may not become apparent until after 5 years of age¹.  
• This process occurs at varying degrees between different populations with East and South-East Asia, tropical Africa and Native Americans and Australians more likely to suffer with lactose malabsorption³.

• Occurs secondary to mucosal damage affecting the production of lactase.
• It is most often following severe gastroenteritis but also in conditions such as coeliac disease and CMA when the epithelium is damaged¹.
• It is usually transient and tolerance to lactose improves again once the epithelial lining has repaired. 

CMA, also known as Cow’s Milk Protein Allergy (CMPA), is an immunologic hypersensitivity to one or more of the proteins found in milk. This allergy is particularly prominent in infants and young children.^1,5 Typically, it presents in early infancy soon after initial exposure to cow’s milk protein in formula or weaning solids but also in a lower incidence of exclusively breastfed infants.^6,7 The prognosis is good with approximately 50% outgrowing their allergy by 5 years of age and 75% of patients outgrowing their milk allergy by adolescence⁸. 

CMA can present as a broad range of symptoms involving many organ systems depending on the type of immune reaction causing the allergic response. Discriminating between the type of reaction is important as it can determine the risk of developing other food allergies and atopic disease⁹.

There are two main types of CMA¹:

• An IgE-mediated (immediate) allergy involving IgE Antibodies. Symptoms start within minutes to 2 hours after allergen ingestion. Symptoms might include urticaria, swollen eyes, lips, breathing difficulties, anaphylaxis, abdominal pain and vomiting¹⁰.
• A Non-IgE-mediated (delayed) allergy which are generally T cell-mediated. Symptoms typically occur after 2 hours and up to 72 hours from allergen ingestion. These may include gastrointestinal symptoms such as reflux, diarrhoea, cramps, constipation or cause eczema and respiratory symptoms¹⁰. Non-IgE CMA can often be dose dependant¹¹ and is perhaps more likely to be misdiagnosed as intolerance due to overlapping gastrointestinal symptoms.

It can sometimes be difficult to differentiate between CMA and lactose intolerance, as some digestive symptoms overlap such as nausea, abdominal pain, and diarrhoea. However, there are some distinct differences to be aware of that can help inform diagnosis and, therefore, ensure correct management.¹