How Dairy Activates the Immune System (And Why That’s a Problem)

Before my third pregnancy, I had been off dairy for about two years and felt fantastic. My digestion was better, my energy levels were stable, and I had no significant skin issues. But during my pregnancy, I started adding dairy back in—because hey, cravings happen.

At first, I didn’t think much of it. But then my lips started swelling.

It was subtle at first—just a little puffiness that I brushed off. But it got worse. My lips became inflamed and sore, like I had a mild allergic reaction. I still didn’t make the connection to dairy. Months later, I developed rashes on my knees and ankles—itchy, persistent, and frustrating.

It wasn’t until a recent consult with biochemist and nutritionist Karen Hurd that I finally put the pieces together. She challenged me to remove dairy again, explaining how undigested casein can enter the bloodstream and trigger an immune response.

Since then, I’ve also been wondering about another symptom I’ve dealt with for years—constant throat clearing and phlegm. It’s one of those things I’ve just learned to live with, but it drives me nuts, and I’m sure the people around me as well. I now suspect this could be dairy-related or inflammation-related. I’m excited to find out if cutting dairy will help eliminate this annoying, chronic issue.

I decided to give dairy-free living another try, and I’m happy to report that my symptoms are improving. My rashes are healing, the itchiness has decreased, and my lips don’t hurt as much as they used to. I’m excited to see how my body continues to heal as I stay dairy-free.

Most people assume lactose (the milk sugar) is the biggest problem with dairy. But for many, casein, the primary protein in milk, is the real issue.

Casein is a large, complex protein that is difficult for humans to fully break down. Unlike other proteins, casein requires a specific set of digestive enzymes (such as chymotrypsin, pepsin, and zymogen) to be broken down properly. However, many people lack the enzymes needed to fully digest casein, especially as they get older.

When casein isn’t fully broken down, it can:

• Enter the bloodstream in a partially undigested form
• Trigger an immune system response
• Cause inflammation, allergic reactions, and autoimmunity

When undigested casein molecules enter the bloodstream, the immune system identifies them as foreign invaders—similar to bacteria or viruses. The body then launches an immune response, producing IgG and IgE antibodies, which trigger mast cells to release histamine and inflammatory cytokines.

This immune activation can lead to:

• Mucus production as the body tries to flush out the invader
• Inflammation in the gut, skin, and respiratory system
• Increased adrenaline levels, which worsen stress responses and nervous system dysregulation

This is why dairy is often linked to asthma, chronic sinus issues, seasonal allergies, and eczema. The body is simply trying to rid itself of what it perceives as an invader.

Once the immune system is activated, inflammatory messengers like histamines, interleukins, and prostaglandins flood the body.

These inflammatory compounds increase vascular permeability, allowing immune cells to reach the affected areas.

But they also contribute to symptoms like:

• Swollen lips and face (like I experienced)
• Itchy, inflamed skin (eczema, psoriasis, rashes)
• Digestive issues (bloating, diarrhea, constipation, gut pain)
• Chronic mucus buildup (constant throat clearing, postnasal drip, congestion)
• Joint pain and stiffness

For me, my swollen lips and rashes were a clear sign that my body was fighting against dairy. The immune system was sending out inflammatory messengers to attack the undigested casein in my bloodstream, leading to the physical symptoms I was experiencing.

The more the immune system is triggered, the more inflammation builds up in the body. Over time, this can lead to autoimmune conditions, where the body starts attacking its own tissues. Some chronic conditions linked to dairy consumption include:

• Asthma and chronic sinus infections
• Eczema, psoriasis, and other skin conditions
• Arthritis and joint pain
• Irritable Bowel Syndrome (IBS) and leaky gut
• Hashimoto’s thyroiditis and other autoimmune diseases

Many people don’t realize that their symptoms are connected to dairy—until they remove it.

I’m not the only one who has experienced health improvements from cutting out dairy. Here are some common benefits people notice after just three weeks without dairy:

• Clearer skin (acne, rashes, and eczema improve)
• Better digestion (bloating, constipation, and diarrhea disappear)
• Reduced inflammation (less joint pain, stiffness, and puffiness)
• Improved breathing (less congestion, mucus, and asthma symptoms)
• More energy (no more sluggishness or post-meal fatigue)

As Karen Hurd explained in our conversation, it takes about three weeks for the liver to fully clear casein from the body. So if you want to see how dairy affects you, give yourself a full three weeks dairy-free and pay attention to your symptoms.

The human body is incredibly intelligent. It communicates with us through symptoms, trying to tell us what is and isn’t working.

When I reintroduced dairy, my body immediately started signaling distress—I just didn’t recognize it at first.

Now that I’ve given up dairy again, my swollen lips and rashes are starting to heal. My experience, along with the science behind dairy’s effects on the immune system, has made it clear: dairy wasn’t serving my body.

And now, I’m excited to see if eliminating dairy will also resolve my chronic throat clearing and phlegm. I’ve lived with it for so long that I almost forgot to question it. But if this is also a symptom of inflammation or immune activation, I can’t wait to see if going dairy-free will finally bring relief.

If you’ve been struggling with chronic inflammation, allergies, skin issues, or gut problems, I encourage you to try removing dairy for three weeks. You might be surprised at how much better you feel.

And if you want to learn more, check out Karen Hurd’s work at www.karenhurd.com. She has an incredible way of explaining nutrition and how food interacts with our bodies.

Have you ever noticed a change in your health after cutting out dairy? I’d love to hear your experiences in the comments!