Dairy sensitivity symptoms: What you should know

By Robert A. Fried, MD Jun 30, 2022 • 4 min

Many people report feeling bloated or ill after consuming dairy, which may indicate a sensitivity to dairy products called milk or lactose intolerance. Lactose intolerance can cause a range of unpleasant symptoms, but it is not life-threatening.

Milk allergy and milk intolerance: What's the difference?

Developing symptoms after consuming milk or dairy products can usually be traced to two possible causes: milk allergy or lactose intolerance.

  • An allergy means the body's immune system is involved. The body reacts as if an allergen, the substance you're allergic to, is a harmful invader and tries to fight it off. True milk allergy is an allergic reaction to a protein found in milk, and the symptoms of milk allergy can range from mild to severe and can be life-threatening.
  • An intolerance doesn't involve the immune system. Lactose intolerance (sometimes referred to as a milk or dairy intolerance) is usually caused by not being able to fully digest lactose, the main sugar found in cow's milk and milk products. Symptoms of dairy intolerance are generally milder.

Milk allergy

When someone is allergic to milk, they're allergic to one or both of the proteins found in milk—casein and whey. Milk allergy, dairy allergy, cow’s milk protein allergy and casein allergy all mean the same thing. Milk allergy almost always starts in childhood and usually begins within a week of a baby's first introduction to cow's milk. About 2.5% of children under age 3 are allergic to milk, and most will outgrow their allergy.

Milk allergy symptoms can start either right away or hours after drinking milk or eating a food that contains milk. Some of the symptoms of milk allergy include:

  • Loose stools or diarrhea 
  • Blood or mucus in the stools 
  • Stomach cramps
  • Vomiting
  • Hives
  • Anaphylaxis. This life-threatening reaction narrows the airways, can block breathing, and send your body into shock. Call 911 right away if you have signs of anaphylaxis.

Atopic dermatitis is often associated with a milk allergy, and it’s often called a milk allergy rash. However, atopic dermatitis is not a milk allergy rash nor is it caused by an allergy to milk. It’s actually a separate autoimmune skin condition. Atopic dermatitis is a form of eczema that can start in infants as young as 2 months old. People usually outgrow atopic dermatitis when they reach early adulthood. Children who have atopic dermatitis are more likely to develop allergies in general, including milk allergies. Children with atopic dermatitis also commonly have a family history of eczema, hay fever or asthma.

Milk intolerance

Unlike milk allergy, intolerance to milk and milk products usually develops after infancy. It can be a problem in toddlers as young as 2 years old, and it sometimes doesn't appear until adolescence or adulthood.

Symptoms of milk intolerance, also known as lactose intolerance, can include:

  • Bloating and gassiness
  • Stomach cramps
  • Diarrhea

Milk intolerance is uncomfortable but not a serious health threat.

Sensitivity to dairy products is a real concern for many people, either for themselves or their children. While the symptoms of milk or lactose intolerance can be uncomfortable and distressing, they are not serious and there are over-the-counter lactose intolerance supplements available. It’s always best to talk with your healthcare provider if you have questions about milk or lactose intolerance.

Published June 2022.