ConditionChildren's health
Milk Allergy (Cow's Milk Allergy)
Milk allergy is an immune reaction to the proteins in cow's milk, mainly casein and whey. It is the most common food allergy in babies and young children, affecting about 2 in 100 infants, and most children outgrow it by school age. Reactions range from hives, vomiting and wheezing within minutes to delayed symptoms such as eczema flares, blood in the stool or reflux. It is different from lactose intolerance, which is a digestive problem with milk sugar. Treatment is avoiding milk protein, with a hypoallergenic formula for formula-fed babies.
Also called: Cow's milk allergy, cow's milk protein allergy (CMPA), dairy allergy, milk protein allergy
At a glance
- What it is
- An immune reaction to cow's milk proteins (casein and whey).
- Who gets it
- Mostly infants and young children; most outgrow it by 3 to 6 years.
- Types
- Immediate (IgE-mediated) and delayed (non-IgE-mediated).
- Symptoms
- Hives, vomiting, wheeze, anaphylaxis; or delayed eczema, diarrhea, blood or mucus in stool, reflux, poor growth.
- Treatment
- Strict avoidance; extensively hydrolyzed or amino acid formula; epinephrine for those at risk of anaphylaxis.
When to get help
Call 911 or go to the ER
- Difficulty breathing, wheezing, hoarse cry, swelling of the lips or tongue, or a baby becoming pale and floppy after milk: use an epinephrine auto-injector if prescribed and call 911 or your local emergency number
- Repeated, projectile vomiting 1 to 4 hours after milk with pallor, lethargy or floppiness (possible FPIES)
See a doctor within a day or two
- Widespread hives or facial swelling after milk, even if it settled
- A baby with bloody diarrhea, signs of dehydration or poor feeding
Book a routine appointment
- Blood or mucus streaks in a baby's stool
- Persistent eczema, reflux, vomiting or colic not improving with usual measures
- Poor weight gain in a baby on cow's milk formula
- Suspected milk allergy in an older child or adult
How milk allergy works
Cow's milk contains two main protein groups: casein (about 80%) and whey (about 20%). In milk allergy, the immune system treats these proteins as harmful.
- IgE-mediated (immediate) allergy: IgE antibodies trigger histamine release within minutes to 2 hours. It can cause anaphylaxis.
- Non-IgE-mediated (delayed) allergy: immune cells in the gut react more slowly, with symptoms appearing hours to days later. This includes allergic proctocolitis and FPIES.
Milk from goats and sheep has very similar proteins and usually causes reactions too.
Symptoms
Immediate reactions
- hives, redness or itching, often around the mouth
- swelling of the lips, face or eyes
- vomiting
- coughing, wheezing, runny nose
- in severe cases, anaphylaxis: breathing difficulty, pallor, floppiness, collapse
Delayed reactions
- worsening eczema
- vomiting and reflux
- diarrhea or constipation
- streaks of blood or mucus in the stool (allergic proctocolitis), usually in a baby who otherwise seems well
- excessive crying or colic-like symptoms
- poor weight gain
Babies can react to cow's milk protein through breast milk if the breastfeeding parent consumes dairy, though this is less common than reactions to formula.
Milk allergy vs lactose intolerance
| Milk allergy | Lactose intolerance | |
|---|---|---|
| Cause | Immune reaction to milk protein | Low lactase enzyme to digest milk sugar |
| Typical age | Infants and young children | Older children and adults; rare in babies |
| Symptoms | Skin, gut and breathing; can be severe | Bloating, gas, cramps, diarrhea only |
| Amount | Tiny amounts can trigger reactions | Related to amount; small amounts often tolerated |
| Lactose-free milk | Not safe | Safe |
Diagnosis
- history: symptoms, timing, what was eaten
- skin prick test or specific IgE blood test for immediate reactions
- elimination and reintroduction: for delayed reactions, removing milk for 2 to 4 weeks and seeing whether symptoms improve, then reintroducing under guidance to confirm
- supervised oral food challenge when the diagnosis is uncertain or to check whether the allergy has resolved
There is no reliable test for delayed milk allergy; diagnosis relies on response to elimination and reintroduction.
Treatment
Formula-fed babies
- extensively hydrolyzed formula: milk proteins are broken into small pieces; suitable for most babies with milk allergy
- amino acid-based formula: for severe reactions, anaphylaxis, FPIES or when hydrolyzed formula fails
- soy formula may be an option for some babies over 6 months without soy allergy, under medical guidance
- partially hydrolyzed ("comfort" or "HA") formulas and lactose-free formulas are not suitable
Breastfed babies
Continue breastfeeding. If the baby has symptoms, the breastfeeding parent may be advised to cut out dairy, with calcium and vitamin D supplements and dietitian support.
Older children and adults
- avoid milk and milk products, and read labels. Milk is a major allergen and must be declared on US food labels
- watch for hidden sources: casein, whey, lactalbumin, butter, ghee, curds and milk solids
- use calcium-fortified alternatives such as soy or pea milk, and ensure enough calcium, vitamin D and protein; a dietitian helps
- carry an epinephrine auto-injector if you have had or are at risk of severe reactions
Baked milk and the milk ladder
Heating changes milk proteins. Many children with milk allergy can tolerate milk baked into muffins or cakes. Under allergist guidance, gradually reintroducing baked then less-processed milk (a "milk ladder") may speed tolerance. Do not try this at home without medical advice if your child has had immediate reactions.
Outlook
Most children with milk allergy outgrow it. Non-IgE allergy usually resolves by 1 to 3 years, and most IgE-mediated milk allergies resolve by school age, though some persist into the teens or adulthood. Allergists recheck tolerance periodically.
Frequently asked questions
What are the symptoms of milk allergy in babies?
Immediate symptoms include hives, swelling, vomiting and wheezing within minutes to 2 hours. Delayed symptoms include eczema, reflux, diarrhea, blood or mucus in the stool, colic and poor weight gain.
What is the difference between milk allergy and lactose intolerance?
Milk allergy is an immune reaction to milk proteins and can cause hives, vomiting, breathing problems and anaphylaxis. Lactose intolerance is difficulty digesting milk sugar and causes only digestive symptoms such as bloating and diarrhea. Lactose-free milk is safe in intolerance but not in allergy.
Which formula is best for milk allergy?
Most babies do well on an extensively hydrolyzed formula. Babies with severe reactions or who still react need an amino acid-based formula. Partially hydrolyzed, lactose-free and goat's milk formulas are not suitable.
Do children outgrow milk allergy?
Most do. Many outgrow delayed-type milk allergy by age 1 to 3, and most immediate-type milk allergy resolves by school age. An allergist can test periodically to see whether milk can be safely reintroduced.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Allergy, Asthma & Immunology: Milk allergy
- American Academy of Pediatrics: Cow's milk allergy and hypoallergenic formulas (HealthyChildren.org)
- World Allergy Organization: DRACMA guideline on cow's milk allergy
- NIAID: Guidelines for the Diagnosis and Management of Food Allergy
- NHS: Cows' milk allergy