Many people notice a pattern in their lives. Every virus circulating in the community seems to find them. A cold moves through the office and they are the first to fall ill. A winter virus sweeps through the family and they struggle to recover while others bounce back quickly.

This pattern is often described casually as having a “poor immune system,” but the biology behind viral susceptibility is far more complex and far more interesting. Immunity is not a single switch that is either on or off. It is an intricate network involving the nervous system, the endocrine system, inflammatory signalling, nutrition, genetics and the microbiome. When these systems are well regulated, the body is able to recognise viruses early and clear them efficiently. When they are under strain, viruses find more opportunity to take hold.

One of the central pieces of this puzzle lies in our inflammatory signalling pathways. During viral infections the immune system releases messenger molecules called cytokines that help coordinate the antiviral response. One of the important genes involved in this process is IFNG, which regulates interferon gamma production. Interferons are critical in the early stages of viral defence, signalling to neighbouring cells that infection is present and activating immune responses designed to limit viral replication.

However, this inflammatory response also interacts with metabolic pathways in the brain and body. When immune signalling increases during infection, tryptophan metabolism is redirected into the kynurenine pathway. Instead of being used to produce serotonin and melatonin, tryptophan is diverted toward immune regulation. This shift partly explains why viral illness often affects mood, cognition and sleep. The body is prioritising immune defence, and neurotransmitter balance temporarily changes as a result.

At the neurological level, this inflammatory signalling can influence the brain’s immune cells, the microglia. When microglia become activated during illness they release cytokines that contribute to the familiar experience of brain fog, fatigue and emotional heaviness during viral infections. The brain is deeply integrated into immune defence, and inflammation within the nervous system is a normal part of the body’s attempt to recover.

Stress physiology adds another important layer to this picture. The hormone cortisol plays a regulatory role in immune function, helping control inflammation and maintain balance within the immune response. When stress becomes chronic, however, cortisol rhythms can become disrupted. Some people experience persistently elevated cortisol levels, which can interfere with antiviral immune signalling. Others develop flattened cortisol rhythms after prolonged stress, leaving inflammatory pathways less well regulated.

This interaction between stress hormones and immune signalling partly explains why people often become ill during periods of intense emotional or psychological pressure. The nervous system and immune system are in continuous dialogue. When the nervous system is under sustained strain, viral susceptibility often increases.

Nutrition also plays a profound role in immune resilience. Vitamin D is particularly important because it acts more like a hormone than a simple nutrient. Immune cells contain vitamin D receptors (VDR), which allow vitamin D to influence the activity of antimicrobial peptides and regulate inflammatory signalling. Adequate vitamin D status helps the immune system mount effective antiviral responses while preventing inflammation from becoming excessive.

Diet more broadly shapes immune function through its impact on inflammation, blood sugar regulation and the microbiome. Diets rich in whole foods, polyphenols, healthy fats and micronutrients support immune signalling and help reduce chronic inflammatory stress within the body.

In my work with patients I often explore these patterns through genetic insights from LifeCode reports, alongside a deeper understanding of nervous system regulation and inflammatory pathways. Genetics does not determine destiny, but it does reveal how an individual’s immune and inflammatory systems may respond to stressors such as infection, environmental toxins or chronic stress.

Understanding these patterns allows immune support to become far more precise. Instead of generic advice to “boost immunity,” we can support the specific biological pathways that influence immune resilience for each person.

Alongside nutritional and lifestyle foundations, I have also supported patients for many years with individually chosen herbal and homeopathic remedies that help regulate immune responses during viral exposure. Traditional plant medicines work by supporting balance within the immune network, helping the body recognise and respond to viral challenges more effectively.

When immune resilience improves, something interesting happens. People do not necessarily avoid every virus circulating around them. That is not how biology works. But they often notice that they recover more quickly, symptoms are milder, and the immune system regains its equilibrium far faster.

The goal is not to create a body that never encounters viruses. The goal is to support a system that is able to recognise them, respond appropriately and restore balance with resilience.