The Short Answer

Secretory IgA (SIgA) are immune cells that line your mucus membranes and act as your body’s first line of defense against viruses, bacteria, toxins, and food sensitivities. Low SIgA levels are common in people with chronic illness and autoimmune conditions, making you more vulnerable to infections and flares. Restoring SIgA is a functional medicine strategy that helps prevent immune overreaction and reduce autoimmune symptoms.

What Is SIgA and Why Does It Matter for Autoimmune Health?

SIgA are immune cells that come between you and the rest of the world. They live in mucus membranes, such as the digestive, respiratory, and urinary tracts, as well as the prostate and vagina. They are found in mucus, tears, saliva, sweat, and breast milk.

SIgA are the first immune cells to encounter foreign invaders and surround them so they don’t enter the bloodstream. This helps prevent the immune system from becoming hyperreactive, which protects you against food intolerances, chemical sensitivities, and autoimmune diseases. For example, in people with Hashimoto’s low thyroid, adequate SIgA helps prevent the immune system from attacking the thyroid gland.

Scientist Aristo Vojdani, PhD, labels SIgA “nature’s vaccine” because of its protective role against not only viruses and bacterial infections, but also yeasts, environmental toxins, and food sensitivities.

Why Low SIgA Is Common in Chronic Illness

Low SIgA levels are surprisingly common, particularly in people with chronic illness and autoimmune conditions. It’s most often seen in those with fatigued adrenals, which present with symptoms of chronic tiredness, low blood sugar, difficulty getting up in the morning, depression, anxiety, salt cravings, and ongoing health challenges. Many autoimmune patients, including those with Hashimoto’s low thyroid, experience some degree of adrenal dysfunction.

Taking corticosteroid medications can also lower SIgA levels, making this a concern if you’re managing autoimmune flares with these drugs.

Low SIgA and Frequent Infections

Low SIgA levels make it more common to get sick frequently. For instance, low SIgA in the respiratory tract allows viruses and bacteria to more easily invade your system. Without adequate mucosal protection, you become vulnerable to colds, flu, and other respiratory infections that can trigger or worsen autoimmune flares.

The Connection Between Low SIgA and Food and Chemical Sensitivities

What’s often more frustrating than frequent infections is how low SIgA raises the risk of food and chemical sensitivities. SIgA plays a major role in whether you can tolerate your environment while appropriately managing pathogens.

With low SIgA to neutralize invaders, your immune system must become more aggressive, like calling in specialized forces because routine defenses have failed. The result is an overreactive immune response that promotes loss of tolerance to foods or chemicals. Many autoimmune patients struggle with multiple food intolerances and environmental sensitivities as a result.

Low SIgA as an Autoimmune Risk Factor

Low SIgA and the hyperreactive immunity it causes raise your risk of developing or worsening autoimmune diseases. This is particularly relevant for conditions such as Hashimoto’s thyroiditis, lupus, and rheumatoid arthritis, where mucosal barrier function plays a central role in immune tolerance.

At RedRiver, we view low SIgA as a modifiable risk factor, one that functional medicine can address through targeted nutritional and lifestyle approaches.