Why are some people more prone to sickness?

September 26, 2025 •

4 min read

Genetics play a significant role in our immune function, with some people inheriting a greater natural defense against illness. Understanding why are some people more prone to sickness involves exploring the complex interplay of inherited traits, environmental exposures, and daily habits that influence immune strength.

Quick Summary

An individual's susceptibility to illness is influenced by a combination of genetics, immune system variations, environmental exposures, and lifestyle factors like stress, sleep, and nutrition. Chronic conditions, age, and exposure history also play key roles in determining how often someone gets sick.

Key Points

Genetics: Your DNA, particularly HLA genes, determines the inherent strength and specificity of your immune response, making some people naturally more resistant to certain pathogens.
Lifestyle Factors: Chronic stress, sleep deprivation, poor nutrition, and excessive alcohol consumption all suppress immune function, increasing susceptibility to illness.
Environmental Exposure: Constant exposure to pollutants and germs, or the opposite lack of exposure in childhood, can influence the robustness of your immune system.
Chronic Health: Underlying conditions such as diabetes, obesity, and autoimmune disorders weaken immune defenses and make you more vulnerable to infections.
Age: Both the very young (immature immune system) and the elderly (waning immune function) are typically more susceptible to illness.
Microbiome Health: A balanced gut microbiome is critical for a strong immune system; a poor diet or antibiotic overuse can disrupt this balance.
Proactive Management: While genetics are fixed, managing stress, sleep, diet, and exercise are powerful tools to bolster your immune resilience and reduce sickness.

The Inner Mechanisms: Genetics and Immune Variation

Your immune system is a complex network of cells, tissues, and organs that work together to defend your body against infection. However, its effectiveness is not uniform across all individuals. Genetic factors are a primary reason for this variation, influencing everything from the production of immune cells to the body's inflammatory response.

The HLA Gene and Immune Response

One of the most significant genetic components affecting immune response is the human leukocyte antigen (HLA) gene complex. Like a fingerprint, everyone's HLA gene assortment is unique, providing a personalized set of immune defense tactics. This genetic diversity means that one person's immune system might be highly effective against one type of virus, while another's might be more susceptible to it. In some cases, specific HLA variants have even been linked to greater resistance against certain severe infections. Conversely, a variant might make an individual more prone to autoimmune disorders, where the body's immune system mistakenly attacks its own healthy cells.

Primary Immunodeficiency Disorders

In some instances, a person can be born with a primary immunodeficiency disorder, a condition caused by inherited genetic defects that impair the immune system's function. These can range from mild to severe and make individuals significantly more susceptible to infections. While often rare, studying these conditions offers valuable insight into the mechanisms of a healthy immune system.

Environmental and Lifestyle Factors

Beyond genetics, a person's lifestyle and environment are critical determinants of immune health. These factors can either bolster or undermine the body's natural defenses over time.

The Impact of Chronic Stress

Psychological stress is a well-documented immunosuppressant. When the body is under constant stress, it releases the hormone cortisol, which, over time, reduces the number of immune cells and increases inflammation. This makes it more difficult for the body to fight off pathogens and can lead to more frequent and severe illnesses. Factors such as loneliness and a negative emotional state can also contribute to a weakened immune response.

Sleep Deprivation and Poor Nutrition

Insufficient and poor-quality sleep significantly weakens the immune system. During sleep, the body produces crucial proteins called cytokines that help regulate the immune response. A lack of sleep can lower the levels of these proteins, making one more vulnerable to viral infections. Similarly, a diet lacking essential vitamins and minerals, such as Vitamin C, Vitamin D, and Zinc, impairs immune function. Poor nutrition is linked to chronic inflammation and metabolic imbalances that further compromise immunity.

Hygiene, Exposure, and the Microbiome

Poor hygiene habits, such as infrequent handwashing, increase exposure to germs. However, the "hygiene hypothesis" suggests that early childhood exposure to a variety of bacteria and viruses can actually strengthen the immune system over time. The gut microbiome, a community of trillions of bacteria in the digestive tract, also plays a central role in immune regulation. Disruptions to this balance, caused by poor diet or excessive antibiotic use, can weaken immune resilience.

Chronic Health Conditions and Age

Certain medical conditions and the natural aging process can also significantly affect a person's vulnerability to sickness.

Underlying Illnesses

Chronic conditions such as diabetes, obesity, and heart disease can impair the immune system. Diabetes, for instance, can weaken immune function due to high blood sugar levels, while obesity is associated with chronic inflammation that compromises the immune response. Conditions like autoimmune disorders also place the immune system under constant, misdirected stress, leaving it with fewer resources to fight off actual infections.

The Role of Age

Both the very young and the elderly have immune systems that are not fully robust. Children's immune systems are still developing and learning to recognize pathogens, while older adults experience a natural decline in immune function with age. This makes both populations more susceptible to infections and more likely to experience complications from them.

A Comparative Look: What Makes Us Different?


Factor	High Susceptibility	Low Susceptibility
Genetics	Specific HLA variants increase vulnerability; inherited immunodeficiency disorders	Favorable HLA variants offer strong pathogen recognition; no underlying genetic conditions
Lifestyle	Chronic stress, poor sleep, nutrient-deficient diet, heavy alcohol use, sedentary life	Effective stress management, 7-9 hours of quality sleep, balanced nutrition, moderate alcohol intake, regular exercise
Environment	Frequent exposure to pollutants, toxins, and high pathogen loads (crowded areas)	Clean air, minimal exposure to environmental toxins, less crowded living conditions
Chronic Health	Diabetes, obesity, autoimmune disorders, chronic respiratory conditions weaken the immune system	Generally healthy with no underlying chronic diseases taxing the immune system
Age	Very young children (immature immune system) and older adults (waning immune function)	Prime adulthood, when the immune system is typically at its peak resilience

Conclusion: Taking Control of Your Health

Our vulnerability to illness is not a matter of pure luck, but a result of many factors working in concert. While you cannot alter your genetic blueprint, you can significantly influence the lifestyle and environmental factors that affect your immune health. By focusing on adequate sleep, stress management, proper nutrition, and regular exercise, you can strengthen your body's defenses and reduce your overall proneness to sickness. Taking proactive steps can tip the balance in your favor and improve your long-term health and well-being.

For more in-depth information on how nutrition affects your immune system, consider consulting reputable health resources like the National Institutes of Health for further reading.

Frequently Asked Questions

Research suggests a link between personality traits and health. For example, a 'disease-prone personality' associated with chronic negative emotions and stress may lead to immunosuppression and a higher risk of stress-related illnesses like heart disease and frequent infections. Conversely, 'self-healing' personality traits like conscientiousness and emotional security are associated with healthier behaviors and stronger immunity.

Not necessarily. While some studies suggest introverts might be more susceptible to certain respiratory infections due to factors like social withdrawal under stress, the link is not clear-cut and depends on many other variables. Introversion does not automatically equate to a weaker immune system. In fact, some research suggests that while extraverts may have a more active immune response to viruses, they may also be exposed to more pathogens due to their social nature.

Even healthy people can get sick due to a variety of factors beyond their control. This can include genetic predispositions, specific HLA gene variations, or unexpected exposure to a particularly virulent pathogen. A temporary dip in immune function caused by acute stress or temporary sleep disruption could also play a role. Some people also live with undiagnosed chronic conditions that tax the immune system.

Lack of adequate sleep is a major factor in weakened immunity. During sleep, the body produces proteins called cytokines that are essential for fighting off infections and inflammation. Not getting enough sleep lowers the production of these protective cytokines, making you more vulnerable to illnesses and slowing your recovery time.

Yes, a poor diet is a significant risk factor. If your body lacks essential nutrients like Vitamin C, Vitamin D, Zinc, and Iron, your immune system cannot function optimally. A diet high in processed foods and sugar can also disrupt the gut microbiome, which is vital for regulating immune responses.

The hygiene hypothesis proposes that a lack of exposure to pathogens and parasites in early childhood can lead to a weaker immune system later in life. The theory suggests that a more sterile environment prevents the immune system from being sufficiently trained to respond properly, potentially contributing to higher rates of allergies and autoimmune diseases.

Yes, chronic stress is well-known to suppress the immune system. Prolonged high levels of the stress hormone cortisol can reduce the number of lymphocytes, the white blood cells that fight infection. This makes it harder for your body to ward off illnesses and can increase both the frequency and severity of infections.