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Lactose intolerance vs milk allergy in kids

Written by Healthwords's team of doctors and pharmacists based in UK | Updated: 16.02.2023 | 4 min read

It’s easy to get confused between an intolerance to lactose, a component of cow’s milk, and an allergy to milk. Both are very common, but each has a different body response, and therefore needs a different approach to treatment. We’ll take you through the key differences, so you know the signs to spot in your child and where to turn next.

What's the difference between an allergy and intolerance?

Lactose is a type of sugar found in cow’s milk and dairy products. Most of us can process and absorb this as it passes through the gut with the help of an enzyme called lactase. We call it an intolerance when we don’t have enough lactase to break lactose down and digest it. Undigested lactose causes symptoms when it’s broken down in the bowel by bacteria.

In contrast, an allergy to cow’s milk provokes the immune system to react to one of the milk proteins, giving a different set of symptoms.

How can I tell which my child has?

Lactose intolerance develops in slightly older children and adults – compared to cow’s milk allergy, it’s much less common in the very young. With an intolerance, undigested lactose passes through, and the activity of gut bacteria to break it down can cause bloating, excessive wind, tummy pain and diarrhoea. This typically occurs a couple of hours after eating dairy products, and sufferers will usually have eaten a fair amount, compared to cow’s milk allergy, where only a small amount can provoke a reaction.

Cow’s milk allergy occurs much younger, usually in babies less than 1-year-old. It’s more common in formula-fed babies, if they aren’t on a special formula, but can occur in breastfed babies as cow’s milk protein passes from the mother's diet.

Symptoms start when the formula or dairy food is first introduced, and babies may get any combination or severity of different problems. Digestive symptoms are common to both allergy and intolerance, but there is less bloating in allergy, and more likely colic or tummy pain, vomiting, diarrhoea or constipation. Skin problems are common, such as a red itchy rash, swelling around the face, lips or eyes, and hay fever symptoms (a blocked or runny nose).

Symptoms may be immediate, within minutes of taking cow’s milk, or delayed, so several hours or even days afterwards. Many children grow out of this allergy – usually by the time they are 5 years old – it's uncommon for this allergy to persist into adulthood.

While we’ve referred to cow’s milk here, formulas based on goat’s milk, or even drinking whole goat’s milk, is not a viable alternative if your child has an allergy. It contains similar proteins, so they are just as likely to react to this.

When should I speak to a doctor?

If you spot any of the above symptoms in your baby or child, you should book an appointment with your doctor. It’s particularly important if you or your health visitor notices that your baby is not growing as quickly as expected (they drop below their centile line on the weight or height chart), if your baby or child has any persistent gut symptoms or persistent or recurring rashes.

It is helpful to write down a food and symptom diary for your child as this can help inform the doctor when you see them and help with determining the diagnosis. For babies, it’s good to get them weighed and measured with your health visitor prior to the appointment, and take your red book with you.

If your doctor agrees that an intolerance or allergy is likely, they may refer you to a specialist allergy service. This is likely to involve a children’s dietician, who will talk you through how to avoid dairy products, and reassess regularly.

At some point, they may suggest reintroducing dairy too, but they will take you through this step-by-step when it comes to it. With a diagnosis, you may be able to get specialist lactose-free or hypoallergenic formula prescribed, and it’s best to only use these under medical supervision.

Can it be life threatening?

Lactose intolerance is never life threatening. In very rare cases, a cow’s milk allergy can be extremely serious. This is because in a severe food allergic reaction there is the potential for something called anaphylaxis to develop, which is life threatening and can develop quickly. They may be coughing, wheezing or have noisy or fast breathing. You may see the face, lips and tongue swelling, but the risk is if the throat swells, blocking the airways. Any signs of sudden onset swelling of the tongue, lips leading to breathing difficulties should be treated as an emergency, you should call 999 for an ambulance.

Related topics

Read about: Food intolerance

Read about: Gluten-free diet and deficiencies

Read about: IBS - triggers and treatments to ease your symptoms

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