Cow's milk allergy: symptoms, diagnosis and management in babies and children

Allergy UK defines cow's milk allergy as an immune system response to proteins in cow's milk, mainly casein and whey. The NHS food allergy page lists cows' milk among the most common allergic foods and explains that a food allergy is caused by the immune system overreacting. A baby is most often affected, and Allergy UK says it is one of the most common childhood food allergies.

It is different from lactose intolerance. Allergy UK notes that milk is made of protein, sugar and fat, and that lactose intolerance concerns the sugar. The NHS lactose intolerance page says it brings tummy pain, bloating, wind, diarrhoea or constipation and sickness a few minutes or hours after lactose, is usually prevented by eating smaller portions of lactose-containing foods or avoiding them; it contrasts this with food allergy, which can cause breathing difficulty, itchy skin and swelling and can be life threatening.

Allergy UK explains that IgE-mediated allergy involves the antibody called IgE, with symptoms that are quick to appear, within minutes or up to two hours after drinking milk. Non-IgE-mediated allergy is the most common type of cow's milk allergy; its symptoms are delayed, typically developing from two hours after consumption and taking up to 72 hours. NICE's guideline for under 19s uses the same split, noting that IgE-mediated reactions are often immediate and non-IgE-mediated reactions are generally delayed.

This matters for diagnosis, because the delayed form has no simple blood or skin test and can look like other everyday problems of infancy.

Allergy UK says symptoms often start in the early weeks and months of life and can affect the skin, the gut and, less commonly, breathing or circulation. It lists skin reactions such as hives, eczema, redness or itching; vomiting, diarrhoea, abdominal pain or discomfort; sneezing, runny nose, coughing, wheezing or shortness of breath; and general fussiness, irritability and refusal to feed.

The charity also stresses that eczema, colic, reflux and diarrhoea are common in infants and milk allergy is only one of several possible causes. NICE's guideline lists, for non-IgE-mediated allergy, features such as atopic eczema, loose or frequent stools, blood or mucus in stools, reflux, colic, food refusal and, in some cases, faltering growth along with gut symptoms, and says to consider food allergy when eczema, reflux or chronic gut symptoms do not respond adequately to treatment. The NHS page for babies adds that reactions to a new food usually happen within minutes, can take up to 2 hours, and in cow's milk allergy can take up to 3 days.

• Skin: hives, redness, itching, eczema that worsens.

• Gut: vomiting, diarrhoea or loose stools, constipation, tummy pain, blood or mucus in stools.

• Breathing and nose: sneezing, runny nose, cough, wheeze.

• Behaviour: irritability, fussiness and food refusal.

The NHS says to call 999 if the lips, mouth, throat or tongue suddenly swell, breathing becomes very fast or difficult, the throat feels tight or swallowing is hard, the skin, tongue or lips turn blue, grey or pale, someone suddenly becomes very confused, drowsy or dizzy or faints, or a child is limp, floppy or not responding as normal. A swollen, raised or itchy rash may accompany these signs. Do not drive yourself to A&E.

If an adrenaline auto-injector or nasal spray has been prescribed, the NHS says to use it immediately in a serious reaction and then call 999 even if the person seems better. Anaphylaxis is a medical emergency.

Allergy UK advises asking a GP or health visitor without delay, who will take an allergy-focused history, a structured set of questions about the baby's symptoms, timing and feeding. NICE says that history should cover the family and personal history of eczema, asthma or allergy, how quickly symptoms start after contact, how long they last, how severe they are, the baby's feeding history, and the mother's diet if breastfeeding. Testing should not be carried out without first taking this history.

For suspected IgE-mediated allergy NICE says to offer a skin prick test and/or blood tests for specific IgE antibodies, to be performed and interpreted by suitably competent clinicians, with skin prick tests done only where anaphylaxis can be managed. Allergy UK says a GP can arrange referral to a children's specialist allergy service for testing and that waiting times depend on where you live.

For suspected non-IgE-mediated allergy, skin prick and blood tests are not helpful, according to Allergy UK. Instead NICE advises a trial elimination of the suspected allergen, normally for between 2 and 6 weeks, followed by reintroduction, with dietitian advice. Formula-fed babies are given a special low-allergy formula, and breastfeeding mothers may be advised to avoid cow's milk in their own diet; Allergy UK describes a trial of up to six weeks.

Allergy UK says that breastfeeding mothers who are advised to exclude cow's milk should continue to breastfeed. For formula-fed babies, extensively hydrolysed formula still contains cow's milk protein, but in smaller pieces that the immune system is less likely to recognise, and most infants with cow's milk allergy tolerate it. If symptoms continue, an amino acid formula, which is not based on cow's milk, is used. These formulas are available on prescription, and the GP, health visitor or dietitian takes into account age, severity of reactions, other allergic conditions and family history.

Goat and sheep milks are not suitable substitutes, according to Allergy UK, because their proteins are so similar to cow's milk proteins. The NHS says babies with cows' milk allergy who are not breastfed may need special formula and that you should talk to your GP about which kind. Allergy UK also notes that hypoallergenic formulas taste and smell different, most babies under three to four months accept the change readily, and a change in stool colour, such as dark green, is normal.

For older infants the NHS says that, when weaning from around 6 months, allergenic foods including cows' milk foods are introduced one at a time, and that families with a known allergy or a history of eczema, asthma or allergy may need to take particular care and talk to their GP or health visitor first.

The NHS says many children outgrow milk or egg allergy, though some allergies can be lifelong, and Allergy UK says most children grow out of cow's milk allergy in early childhood. In a small number the allergy persists into adulthood, where reactions are more likely to be severe, says Allergy UK.

When the time is right the GP or allergy specialist, usually with a dietitian, discusses reintroducing milk. A milk ladder is a step-by-step method. It starts with baked milk, where the protein has been heavily heated such as in a biscuit, moves to cooked milk and finally uncooked milk. Allergy UK says the ladder is intended for infants with non-IgE-mediated allergy, so it should only be started with clinician guidance.