Effect of Stress on the Immune System

Lesson objective:

Are there beneficial effects to stress? In this lesson we learn about the potential positive impacts that nonchronic stress has on the immune system. We also discuss the competing effects that are carried by chronic stress.

As chronic stress affects your cardiovascular, respiratory, and gastrointestinal system, it also affects the immune system,   

The immune system changes as stress levels rise and stress becomes chronic. 

As discussed, various hormones prepare the cardiovascular, muscular, and endocrine systems to either fight or run, but they also profoundly impact the immune system.  

The cells in your immune system mobilize to attack disease-causing organisms and facilitate emergency repair processes like clotting and inflammation. 

Generally, stimulation of the immune system can be incredibly useful during acute and short-term situations of stress, as high immune functioning helps you avoid infections and heal wounds. Importantly, the duration of exposure to stress – whether physical or emotional– can have directly competing effects on the overall health and wellness of the stressed individual. 

In other words, short term exposure to stress can result in helpful, adaptive immune responses, whereas long-term or repeated exposure to stress can chip away at immune health. 

It is now widely accepted that the immediate response to a stressful event, whether a broken bone or a broken heart, involves an activation and redistribution across the body of specific immune cells and inflammatory markers, which are specific proteins in blood plasma that are released in advance of inflammation. In the minutes following the triggering stressful incident, levels of immune cells (including neutrophils, lymphocytes, helper T cells, and B cells) are all increased in the blood.


Stress hormones then “direct” these circulating cells and factors to exit the bloodstream and enter the skin, the lining of the gastrointestinal tract, the lungs, and other potential “front lines” that may be injured or violated. 

It is understood that these cells all contribute to increased immune function following a stressful event, as if the body is mobilizing in the present to fill an immediate future need to fight off infections, heal wounds, or combat other potential injuries and invasions.

All of this makes sense, and is quite logical. Think about it, for most mammals, most threats to our safety are external, not internal, and the human body has learned to respond accordingly. For most species, the most frequent and likely source of industry is some form of predatory attack, so our immune systems have developed to respond to these likely scenarios. 

If attacked at the skin, immune cells would be crucial in healing a cut and protecting against bacteria entering a wound in the external flesh. Overall, then, the stress response of the immune system basically can be likened to a commander sending troops to the front lines of defense, to protect impending areas of attack, or to rapidly rebuild defenses in the event that initial lines are breached by invaders. 

In a context of chronic stress, however, the HPA axis begins its response to stress by regulating and “turning down” these immune system enhancements. If a stressor persists and becomes chronic, the initially helpful inflammatory response also persists, while overall immune function declines.

Over time, the continued release of cortisol suppresses certain proteins needed to produce new immune cells, called lymphocytes.  Additionally, over time, the immune cells originally mobilized by cortisol grow insensitive to cortisol’s signals.

In other words, over time, immune cells stop “listening” to cortisol, as cortisol is intended to give only short-term mobilization tasks. 

In this way, chronic stress can weaken the overall functioning of the immune system, increasing the likelihood of illness and chronic inflammation.

The combination of ongoing inflammation and decreased immune function can have damaging consequences. 

In fact, the persistent inflammatory response associated with chronic stress has been linked to increased risk of developing depression, cancer, cardiovascular disease, and obesity. 

Also, multiple studies have suggested that there is a relationship between feelings of stress, extreme sadness and difficulty for the body to fight off diseases like colds or the flu. 

Additionally, in conditions of chronic stress, it takes a longer time for the body to heal itself from cuts or bruises.

Researchers are still discovering the intricate ways in which stress interacts with our immune system, and it will take many years before we understand the full picture. We do know with relative certainty that, in the short term, the immune system’s response to stress can be incredibly useful, since the immune system prevents infection and accelerates healing. When stress is continued and becomes chronic, however, the constant release of stress hormones will eventually weaken your immune system, making it a lot harder for your body to respond to pathogens and invasions.