The Brain’s Role in Immune Health

Made up of structural barriers, organs, white blood cells, proteins, and chemicals, the immune system protects us from foreign antigens and helps our bodies heal from infections and injuries. To do this, the immune system and the nervous system maintain extensive and elaborate communication.

“The brain communicates with the immune system through the autonomic nervous system,” says naturopathic doctor Tanja Wright, co-owner of the Vancouver Naturopathic Clinic.

“This system is functioning 24/7 without our conscious control. [It] has two pathways, a gas pedal (flight or fight pathway) and a brake (rest and digest pathway). The neural pathways release chemicals known as neurotransmitters … that influence how the immune cells will behave. [T]he brain can actually tell immune cells to become more active or to calm down.”

The brain reacts to stress by activating the body’s natural alarm system to prepare it for action. “[S]tress causes the brain to release chemicals like cortisol, our stress hormone,” Wright says. But chronic stress can weaken the immune system because, over time, too much cortisol can suppress the immune response, making it harder for the body to fight off infections or heal from injury.

We know that the brain influences the process of inflammation as part of the immune system’s fight against injury or infection. “… but too much inflammation can lead to problems, like chronic pain or diseases,” Wright says. “The brain can help keep this in check but, if it’s overwhelmed by too much stress or illness, inflammation … can cause harm.”

What does the brain have to do with allergies?

The brain is always “on alert,” scanning the body for foreign substances (allergens) that could cause harm to one’s health.

The body’s allergic response

In some cases, the immune system reacts by making antibodies to attack allergens that aren’t otherwise harmful. When someone with an allergy is exposed to the allergen, the immune system’s antibodies release histamine into the bloodstream that can cause symptoms, including inflamed skin, sinuses, airways, or digestive systems.

Overview of allergies

Allergy symptoms can occur for the first time at any age, and can be affected by hormones, stress, smoke, medications, perfume, or environmental irritants. Some allergies can be outgrown, such as children’s allergies to certain foods. Airborne allergens can strike seasonally, during pollination, or year-round in the case of dust mites and animal dander.

The brain’s role

“The brain plays a key role in the allergic response by directing the immune system how to respond,” Wright says. During times of stress, illness, or other factors, such as hormonal changes, our immune systems may be weakened, causing allergic reactions to be more severe.

The brain’s inflammatory response to allergens becomes chronic with repeated exposures to the allergen, which creates long-term effects on the affected areas of the body, such as airways, eyes, and skin. “The brain helps regulate inflammation, but when there’s a lot of inflammation, either from multiple allergies or other factors, like stress or illness, the brain struggles to keep it in check,” Wright says.

Brain health ties to allergies

Poor lifestyle habits can lead to poor brain health which, in turn, can result in higher sensitivity to allergens and more allergic reactions. Wright points to things like lack of sleep, improper diet, chronic stress, and sedentary lifestyle which can cause our immune system to be more reactive.

Alex Chan, naturopathic doctor at Integrative Naturopathic Medical Centre in Vancouver, agrees that daily practices like getting seven hours of quality sleep a night can help boost brain and immune health.

Chen also provides these other strategies for maintaining the health of our brains and, thus, our immune systems:

• Engage in regular exercise and physical activity, which improves circulation and oxygenation and can help strengthen the connections between memory-forming cells.
• Avoid excess alcohol, smoking, and other chemical exposures that impact neurotransmitter levels and damage brain tissue.
• Continue to challenge our brains as we age by learning new things, staying socially engaged, and promoting new neural connections.
• Stay aware of the impacts that common diseases like high blood pressure, diabetes, and inflammation can have on brain health.
• Ensure a well-balanced diet, one that avoids excess neurostimulants, like caffeine, and chemicals, like MSG, and focuses on antioxidant-rich vegetables, healthy omega oils, and optimal hydration.

This article was originally published in the April 2025 issue of alive magazine.