Five signs of a strong immune system according to experts – and how to boost it

We often judge our immune systems based on how many colds we catch in a year, but experts say that’s an oversimplification of what is a highly complex network of cells, tissues and organs that works together to defend the body against foreign invaders.

“The immune system is not a single pathway,” explains Dr Jenna Macciochi, immunologist and author. “It involves multiple layers of defence that work together. These include physical barriers such as the skin and gut lining, the innate immune system which provides rapid early responses to threats, and the adaptive immune system which learns from previous exposures and builds longer-term immune memory.”

“immune health”: “If 10 healthy people are infected with a virus, some may have no symptoms while others feel quite unwell. With a different virus, the pattern may reverse. This natural variation makes it hard to judge immune health from how you respond to a cold.” More broadly, however, “your immune system is influenced by your overall health”,

“Some people – regardless of what they do – will develop disease based on their genetics and environmental factors. While in some cases we can delay the development of disease, we can’t completely prevent disease.”

Signs of a well-functioning immune system

While there isn’t a single visible marker of immune health, certain patterns may suggest that the system is functioning efficiently, Dr Macciochi notes. “It’s important to remember that these are broad patterns rather than diagnostic indicators,” she says.

Quick recovery from infections

“Most adults will still catch colds from time to time. A well-regulated system doesn’t necessarily prevent exposure, but it may help you clear infections efficiently, meaning symptoms resolve in a reasonable timeframe without complications.”

Small wounds heal easily

“The immune system plays a central role in wound healing. Efficient immune responses help control infection risk and coordinate the repair process, so cuts or scrapes tend to close and recover in a typical timeframe.”

Smooth and stable digestion

“A large proportion of immune activity occurs in the gut. While occasional digestive upset is normal, generally stable gastrointestinal function can reflect a well-balanced interaction between the immune system and the gut microbiome.”

Minimal inflammation

“The immune system is responsible for inflammation, but it should also be able to switch that response off. Constant low-grade inflammation or frequent inflammatory flare-ups may indicate that immune regulation is not functioning optimally.”

Consistent energy levels

You generally feel able to maintain consistent energy and recover from everyday stressors.

“Immune activity requires significant energy and coordination with other systems such as the nervous and endocrine systems. While many factors influence energy levels, chronic immune activation or frequent illness can place additional strain on the body.”

How to support immune health

Limited stress

“The one lifestyle factor which most scientists agree will affect your immune health is long-term stress,” Davis says. “There is abundant evidence that stress affects immune health. Stress increases cortisol levels, which dampen immune responses. Stress is part of life and not entirely avoidable, but managing or limiting chronic long-term stress is important.”

Routine vaccines

“Vaccines train our immune systems,” says Bernard. “Vaccines introduce a harmless version or piece of a pathogen (virus or bacteria) into our body to give our immune system something to train on. Vaccines allow our body to practice and build protection so that if we encounter the infectious pathogen out in real life, our immune system is ready to fight and defend us. Vaccines are like seat belts – while they may not prevent the “crash” (infection), they provide protection from serious harm and death.”

Prioritise sleep

“Sleep is one of the most powerful regulators of immune function,” according to Dr Macciochi. “During sleep, the body coordinates immune signalling and memory formation that help it respond more effectively to pathogens in the future. Even small improvements in sleep consistency can make a meaningful difference.”

A rich and varied diet

“The immune system relies on a wide range of nutrients, fibre and plant compounds that support both immune cells and the gut microbiome,” Machiochi says. “A dietary pattern rich in whole foods, particularly vegetables, fruit, legumes, nuts, seeds and high-quality fats such as extra virgin olive oil. Omega-3s and vitamin D are also important.”

Tuned-in symptoms

“Many of the symptoms we associate with illness, such as fever, fatigue, inflammation or a runny nose, are actually part of the immune system’s defence strategy,” Macciochi says. “They reflect the body activating protective pathways.

“While medications absolutely have an important role, particularly when symptoms are severe or prolonged, it’s not always necessary to suppress every mild symptom immediately. Sometimes those signals are simply evidence that the immune system is doing its job. We should see them as information. Do we need to slow down or adjust our lives?

“Immune health isn’t about chasing perfection or never getting sick. It’s about supporting the system that allows your body to respond, adapt and recover effectively over time.”