What is the difference between lactose intolerance and milk allergy?

Around 1 in 10 young children have a reaction when they drink cow's milk. This could be because they have a lactose intolerance or a milk allergy. Milk allergy is much more common than lactose intolerance in children under 5 years of age.

Lactose intolerance is a problem with the digestive system — it means your child doesn't have the enzyme needed to digest lactose, which is the sugar naturally present in milk.

Milk allergy, however, is a problem with the immune system, where the body reacts to the protein in milk. An allergy usually involves other parts of the body as well as the stomach and may cause symptoms such as a skin rash or swelling of the face.

Many young children grow out of their intolerance or allergy. But don’t start giving them milk until your doctor tells you it’s safe to do so.

How do I know if my child is lactose intolerant or has a milk allergy?

Your doctor can confirm whether your child is lactose intolerant or has a milk allergy by asking about your child’s symptoms and doing medical tests. Don’t remove milk or milk-based foods from your child’s diet unless your doctor has told you to.

Don’t use unproven tests such as Vega, kinesiology, Alcat or allergy elimination tests for children. A milk intolerance is very unlikely to be the cause of mucus or coughing.

What causes lactose intolerance?

Lactose is the sugar found in the milk produced by all mammals, including humans. Sometimes, people don’t produce enough of the enzyme lactase in their gut to break down the lactose.

Very few babies have true lactose intolerance, a rare genetic condition where they’re born without any lactase enzymes at all. (This is called primary lactose intolerance.) However, many people develop lactose intolerance later in life, after the age of 5 years. It is more common among Aboriginal and/or Torres Strait Islander people and people from Asia, Africa, the Middle East and some Mediterranean countries.

Lactose intolerance is rare in babies and young children. However, they can become temporarily intolerant to milk if the lining of their gut is damaged by an illness such as gastroenteritis, or an allergy or intolerance to another food. This is called secondary lactose intolerance and will resolve once the gut heals, usually over a few months.

What are the symptoms of lactose intolerance?

The symptoms of lactose intolerance in babies and children are:

• liquid, frothy stools (poo), which may be green
• being irritable
• stomach aches
• bloating
• passing a lot of gas
• slow weight gain
• nappy rash

All of these symptoms are common in babies and don't necessarily mean they have lactose intolerance. But if your child has persistent diarrhoea or isn't putting on weight, see your doctor. Don't stop breastfeeding unless your doctor tells you to.

How is lactose intolerance diagnosed?

Your doctor may suggest cutting out dairy from your child’s diet to see if their symptoms improve. This is known as an elimination diet.

Tests may also include a breath test to measure the hydrogen in your child’s breath, though this test may not be very helpful for young babies (under 3 months old).

How is lactose intolerance treated?

If the lactose intolerance is caused by a tummy upset, keep on breastfeeding. If your baby is formula fed, talk to your doctor or child and family health nurse before switching to low-lactose or lactose-free formula.

Older children will need to cut down on, but not eliminate, dairy foods from their diet. They can still have some cheeses, yogurt, calcium-fortified soy products, lactose-free milk, butter and cream. Your doctor or a dietitian will advise you on the best diet for your child.

Most of the time, young children will recover from lactose intolerance after a few weeks of having a low-lactose diet. Speak to your doctor or dietitian about how to slowly reintroduce milk and dairy products into your child’s diet.

What causes milk allergy?

Milk allergy occurs when your child's immune system reacts to the protein in milk. It is one of the most common food allergies in young children. Most children outgrow milk allergy by the time they reach school age.

What are the symptoms of cow’s milk allergy?

Reactions to milk can occur within minutes or several hours.

Rapid reactions include:

• hives (urticaria)
• swelling of the lips, face or eyes
• stomach pain
• vomiting or diarrhoea
• noisy breathing, wheezing or hoarseness
• a swollen tongue or throat
• change in consciousness or floppiness in babies or young children

Delayed reactions include:

• an increase in eczema
• vomiting and/or diarrhoea that starts 2 to 24 hours after having milk

How is milk allergy diagnosed?

It is very important to see a doctor if your child has the symptoms of milk allergy. Your doctor will ask about your child’s symptoms. They may also refer your child for blood or skin allergy tests.

How is milk allergy treated?

If your child is allergic to milk, you need to completely remove dairy products from their diet. Follow your doctor's or allergy specialist's advice and read food labels carefully. You may also need to avoid milk from other animals, such as goats. You should use coconut products with caution, as many coconut products (especially those from South East Asia) may be contaminated with cow’s milk.

Watch out for other words used to describe milk on food labels, such as butter, buttermilk, cream, curd, ghee, milk, cheese, dairy, milk solids, whey, yoghurt, casein and caseinates.

If your baby is formula-fed, you can use extensively hydrolysed formula (EHF) or amino acid-based formula (AAF). If your baby is over 6 months old, you can also use soy protein formula (unless they are also allergic to soy). Do not use formula made from cow's milk, goat's milk, sheep's milk, HA or A2 milk or lactose-free formulas.

If your child is over the age of one, they can be given soy milk, or calcium-enriched rice, oat or nut milks. It is important to make sure they are getting enough calcium.

If your child is allergic to milk, you may be advised to carry an adrenaline autoinjector (EpiPen® and Anapen®). Severe allergic reactions can sometimes lead to anaphylaxis, which is an emergency and can even be fatal. An adrenaline autoinjector can be used to give first aid in the event of anaphylaxis.

Can I still breastfeed my baby if they are lactose intolerant?

If your baby is lactose intolerant, you can continue to breastfeed without changing your diet. Reducing the amount of dairy you consume will not reduce the amount of lactose in your breastmilk.

Can I still breastfeed my baby who has a milk allergy?

Breastmilk is best, including for babies who have a milk allergy. In some cases, your doctor may advise you to remove milk and dairy products from your own diet. In other cases, you may be able to eat your regular diet. Your doctor or allergy specialist will advise you.

Resources and support

Speak to your doctor or child health nurse for more information on allergy foods.

'Nip Allergies in the Bub' is an initiative from the National Allergy Strategy that has information for both parents and health professionals.

Learn more about allergies from the Australasian Society of Clinical Immunology and Allergy.

Read more about avoiding food allergies in babies from the Royal Australian College of General Practitioners.