If you don't feel well after eating dairy products, you're not alone. Around 30 million Americans have some degree of lactose intolerance and while it's rarely dangerous, the symptoms, which include abdominal pain, gas, and diarrhea, can definitely be unpleasant and inconvenient. But what other symptoms should you look out for, and how can you mitigate them? Let's take a look at the science. (Source) 

What Is Lactose Intolerance and What Causes It? 

Your small intestine produces an enzyme known as lactase, which breaks down lactose, the natural sugar present in milk and dairy products. If your body doesn't make enough lactase, it's harder for you to break down lactose and you'll experience what’s known as lactose malabsorption.

When lactose malabsorption causes GI symptoms such as bloating, pain, and diarrhea, this is known as lactose intolerance. Not everyone with lactose malabsorption has symptoms of intolerance after consuming dairy, and even those with lactose intolerance may be able to have a small amount of dairy before they start experiencing symptoms

Lactose intolerance is often genetic, but can also be caused by: 

• injury to the small intestine: This can include infections, as well as Crohn's disease and celiac disease, or other conditions that result in the intestine generating less lactase than it should. 
• treatments such as radiation therapy and surgery: This kind of injury to the small intestine can affect the amount of lactase being made. When lactose intolerance is caused by an injury to the intestines it's called secondary lactose intolerance, and can sometimes be reversed if the injury can be treated. 
• premature birth: Lactose intolerance at birth is usually a temporary condition that resolves when the small intestine begins to make more lactase. 
• lactase non-persistence: Some people produce enough lactase to tolerate dairy while they are very young, but lose their tolerance in adulthood as their lactase production drops. While being unable to digest cow’s milk, they may still be able to enjoy dairy products such as yogurt and cheese, because the fermentation involved in making  these items breaks down the lactose. 

(Source, Source, Source)

What's the Difference Between Lactose Intolerance and a Milk Allergy? 

Lactose intolerance and a milk allergy are two distinctly different things. A milk allergy develops within the first year of life, whereas lactose intolerance usually develops over time as production of lactase falls. While lactose intolerance is caused by a lack of the enzyme necessary to digest dairy and doesn't involve the immune system at all, a milk allergy is an immune disorder in which the immune system reacts to the proteins found in milk and products that contain it. 

The symptoms of lactose intolerance are also different from those of a milk allergy. Let's have a closer look. 

Symptoms of Lactose Intolerance 

These symptoms are commonly associated with lactose intolerance: 

• diarrhea
• nausea, sometimes with vomiting
• abdominal cramps and bloating 
• flatulence 

Symptoms of a Milk Allergy

The symptoms of a milk allergy, which set in immediately, include: 

• wheezing 
• hives 
• vomiting 
• itching and tingling around the mouth and lips 
• swelling in the mouth, throat, and lips 
• shortness of breath
• coughing 

You can also develop these symptoms of a milk allergy over time: 

• watery eyes 
• runny nose 
• diarrhea, which may contain blood 
• abdominal cramps 

Lactose intolerance isn't dangerous, but a milk allergy can cause anaphylaxis, a severe reaction that can cause constriction of the airways, as well as: 

• sudden reddening of the face 
• a drop in blood pressure 
• swelling of the throat
• difficulty breathing 

(Source, Source) 

Dairy and Inflammation

An allergy is an immune system response during which the body generates antibodies to attack an allergen, or substance, that's seen as a threat. The initial reaction includes symptoms such as hives or gastrointestinal reactions, and some people experience a late phase reaction with symptoms such as pain and redness. If exposure to the allergen happens consistently, chronic inflammation can develop. 

There's conflicting information as to whether or not dairy itself causes inflammation. In a 2021 study, yogurt was actually shown to reduce inflammation, due to its probiotics, while another study indicated that cheese might have a proinflammatory effect. A 2017 review of 50 clinical trials found that neither low- and full-fat dairy products increased inflammation. (Source, Source, Source)

For those with milk allergies, milk triggers inflammation. For example, allergic colitis is a condition in children in which inflammation in the colon is caused by a reaction to cow's milk, and treatment involves starting a milk-free diet. (Source, Source)

The Unexpected Symptoms of a Milk Allergy 

Did seeing "runny nose" as a symptom of a milk allergy above throw you off? Well, it's one of two symptoms of a milk allergy that might come as a surprise. 

Skin Inflammation  

If you thought you'd left acne behind in puberty but you continue to see it into adulthood, there could be something more to it, including a milk allergy. Since cow's milk does lead to inflammation in those with a milk allergy, it's possible that the inflammation leads to clogged pores, which can cause acne.

Milk also increases the activity of the naturally occurring hormone IGF-1, or insulin-like growth factor 1, which can lead to the generation of more sebum oil, a cause of acne. While all types of dairy milk (whole, skim, and low fat) are associated with acne breakouts, that isn't the case with yogurt, cheese, or other products that are made from milk. (Source)

For those with atopic dermatitis, a common type of eczema, breakouts are often associated with food allergies, including dairy. (Source)

Nasal Issues 

Milk allergies are usually associated with gastrointestinal inflammation-related symptoms, but you might also experience others, such as a runny or blocked nose. Allergic rhinitis is a condition that occurs when your immune system decides to react to an allergen, causing the mucus membranes in your nose to swell and excess mucus to be produced. When allergic rhinitis isn't addressed, it can result in: 

• sinusitis, or inflammation of the sinuses that can develop when swelling of the nasal passages stops mucus from draining out of them
• infection of the middle ear, the part of the ear right behind the eardrum 
• nasal polyps, which are benign sacs of fluid that grow inside the nasal passages and sinuses. In one study of a group of patients with both chronic sinusitis and nasal polyps, 14% were also found to have an allergy to milk. 

(Source, Source) 

Managing a Milk Allergy 

Negotiating a milk allergy can be tricky, because milk and the milk proteins casein and whey are present in foods you might not suspect would contain them. There are means of addressing a milk allergy, however. 

Non-dairy Milk Alternatives 

There's good news if you have a milk allergy -- a plethora of non-dairy milk alternatives are available, such as: 

• coconut milk 
• tiger nut milk 
• nut milks (almond, cashew, hazelnut) 

The most important thing to consider when looking for a milk alternative is that you're able to digest it. Making your own non-dairy milks can be a good option to be sure that you're getting a beverage that doesn't accidentally contain any milk proteins (see below). Your health care provider may also recommend a calcium supplement. 

(Source, Source) 

Foods That Are Rich in Calcium

The following foods are rich in calcium and don't include milk or milk proteins:

• dark green vegetables, such as collard greens and kale
• broccoli rabe and broccoli 
• bok choy
• seafood, including salmon, sardines, and shrimp
• foods fortified with calcium, such as almond milk, orange juice, and oatmeal 

(Source, Source)

Eliminating dairy from your diet can have nutritional consequences, because it contains calcium, vitamin D and other nutrients that are essential for maintaining health and adequate nutrition. If you’ve been relying on dairy products to meet your nutritional needs, you’ll need to be sure you get adequate amounts of calcium from other sources. 

When you don't get enough calcium and vitamin D, you may be at risk for: 

• conditions that affect the bones, such as osteoporosis, rickets, and osteomalacia
• pre-eclampsia, a dangerous pregnancy complication during which a pregnant person develops high blood pressure and protein in the urine. Studies have shown that calcium supplementation helps maintain healthy blood pressure in pregnancy, and supplementing with vitamin D can help reduce risk of pre-eclampsia. 

(Source, Source, Source) 

Avoid Accidental Milk Product Ingestion

Be sure to carefully read food labels in order to avoid accidentally ingesting milk products. Keep an eye out and steer clear of foods that contain: 

• whey and whey protein (including its components lactalbumin, lactoglobulin, and lactoferrin), made from the liquid that's leftover after milk is strained and curdled 
• casein, the chief milk protein found in yogurt, cheese, dietary supplements, and infant formula
• rennet casein, found in melted and processed cheeses 
• nougat
• margarine 
• natural, caramel, and brown sugar flavorings 
• chocolate 
• lactic acid starter culture, found in fermented food products
• Simplesse, a protein-based fat substitute made from milk proteins and used in low calorie and low sugar drinks, creamers, dressings, soups, sauces, ice cream, and powdered mixes. 

(Source, Source, Source) 

Oral Immunotherapy

Oral immunotherapy, in which a patient is exposed to increasing amounts of a food allergen over time until a full serving is tolerated, is a new approach to treating food allergies. In addition to desensitizing the body to the allergen, it can also improve quality of life by reducing anxiety about having a dangerous reaction if you accidentally eat something that triggers your allergy. 

In treating milk allergies, oral immunotherapy can include the use of an anti-IgE monoclonal antibody that suppresses severe allergic reactions, as well as omalizumab, an anti-inflammatory drug for allergic asthma. More research is needed to assess the long-term impact of oral immunotherapy. (Source, Source)

The Bottom Line  

Lactose intolerance can cause uncomfortable intestinal symptoms but isn't dangerous. A milk allergy, on the other hand, can cause symptoms ranging from a runny nose to life-threatening anaphylaxis. The difference between them is that lactose intolerance has nothing to do with inflammation or an immune system reaction, whereas a milk allergy involves both. Skin inflammation (acne, or, if you have atopic dermatitis, a flare-up) and nasal issues can also indicate inflammation associated with milk products. Depending on the severity of your reaction, you may be encouraged to entirely eliminate milk or other dairy products, which can be challenging. WellTheory's Care Team is here to support you in making diet and lifestyle changes, evaluating next steps, and finding a community of others who share your experiences.