Why Do I Keep Getting Sick? Factors That Determine Immunity

Despite healthy habits, some people are likely to get sick more often than others.

Even if you're generally healthy, there's always the possibility of getting sick. However, how often you get sick as a healthy person depends on how your body functions.

If you are wondering why you are getting sick, learn how several factors affect your immune system, including lifestyle choices, environment, genetics, and age. Also, you have different types of immunity, affecting your likelihood of getting sick. 

"I have some perfectly healthy patients who get five to six upper respiratory infections—the common cold, or more rarely, full-blown influenza—a year, and others with the same health profile who hardly ever get sick," Holly Phillips, MD, an internist based in New York, told Health.

Here's what you should know about immunity and what affects your susceptibility to infections.

Types of Immunity

Your immune system protects you from illnesses and helps fight germs when you get sick. Different types of immunity may affect how likely you are to get sick.

"Immunological genes are many and complex, and your immune response depends on their combined performance," Paolo Boffetta, MD, professor of medicine, hematology, and medical oncology at the Icahn School of Medicine at Mount Sinai, told Health.

For instance, your active immunity builds up when you come into contact with germs. Your immune system responds by creating antibodies that protect you from those germs in the future. You can also build your active immunity through vaccination. 

In contrast, passive immunity is when antibodies produced outside your body become part of your immune system. For example, a fetus receives antibodies from the mother via the placenta during pregnancy.

"There are factors during infancy and childhood, and perhaps also in utero, that contribute to the development of the immune system, but they are not fully understood," said Dr. Boffetta.

You also have innate immunity, the immunity you are born with. Innate immunity includes any aspect of the body's defense against microbes and pathogens, such as cough reflexes, mucus, and stomach acid.

What Can Negatively Affect the Immune System?

Several lifestyle factors can weaken your immune system and lead to frequent infections.


Stress is your body and brain's ability to respond to challenges or demands.

During stressful times, your body releases a hormone called cortisol. Generally, short-term stress is less harmful to your health than chronic stress. Immediately, high cortisol levels may protect your immune system by reducing inflammation in the body.

However, being stressed for long periods can adversely affect your immune system. For example, as cortisol levels stay high, your body adapts, increasing inflammation. Also, stress reduces immune cells, called lymphocytes. Without enough lymphocytes ready to fight illnesses, you might be sick often. 


Obesity can also play a part in a weak immune system. For example, people with obesity are more likely to be sick with COVID-19 and have severe symptoms than others.

Obesity is a risk factor for cardiovascular disease. Therefore, people with obesity might have related conditions like high blood pressure or coronary artery disease (CAD). These underlying health conditions further weaken the immune system. 

Obesity increases inflammation and cytokine levels. Cytokines are proteins that help fight infections. However, excess cytokines are harmful because they may weaken your immune system and worsen symptoms.

Alcohol Use

The occasional alcoholic drink may not cause many issues for your immune system. However, engaging in frequent or chronic heavy alcoholic drinking can reduce the efficiency of your immune system.

For example, alcohol use disorder is linked to reduced immune cell frequency. You may be sick often without enough immune cells ready to fight infections.


Air pollution can harm the immune and cardiovascular systems at a young age. Thus, environmental factors, such as pollutants and toxins, may weaken your immune system over time, even during childhood.

Air pollution can trigger the immune system to unnecessarily react, such as in asthma, or interfere with an immune response, as seen in the dysregulation of anti-viral responses.

Who’s More at Risk of Being Sick Often?

In addition to a lifestyle that may negatively impact your immune system, other aspects may affect how often you get sick. Several factors determine your immunity, such as:

  • Genetics: Genetics play a significant role, explained Dr. Boffetta. For example, your genetics can determine your innate immunity. Weak innate immunity wanes your active immunity and increases your risk of infections.
  • Age: Older adults tend to have weaker immunity than younger adults. Around age 60, the immune system wanes, opening the door for germs to more easily or severely affect you.
  • Season: The time of the year may also affect how easily you get sick. For example, you may get sick with the flu or a cold during winter. This is because cold weather helps viruses spread easily. Also, you may be huddled indoors, close to others, during that time. Close proximity also increases the risk of viruses spreading.
  • Exposure: The hygiene hypothesis may explain why some people are more susceptible to illness. The idea is that the more bacteria and viruses you encounter as a child, the "stronger" your immune system becomes.

How To Strengthen Your Immune System

Although you cannot entirely boost your immunity, healthy habits can help protect you from illnesses:

  • Eat a healthy diet: Nutrients from fruits and vegetables, like zinc, iron, vitamin C, and omega-3 fatty acids, are essential for a healthy immune system. For example, omega-3 fatty acids in fatty fish help produce immune cells.
  • Exercise regularly: Physical activity improves circulation, which helps produce germ-fighting antibodies. Also, exercise reduces stress, which helps your immune system function.
  • Get enough sleep: While sleeping, your body releases cytokines, proteins that help fight infections and control your stress response. A lack of sleep can reduce cytokine levels, increasing your risk of illnesses.
  • Manage your weight: Obesity may affect your immunity, so maintaining a healthy body weight may strengthen your immune system. Obesity also raises the risk of chronic illnesses, like diabetes and cardiovascular disease, which weaken immunity. 
  • Reduce stress levels: If you have chronic stress, try stress-relieving activities to lower your cortisol levels. Deep breathing, meditation, and listening to calm music may help control stress.
  • Quit smoking: Smoking may raise the risk of respiratory complications if you get sick.
  • Limit your alcohol intake: Moderate alcohol consumption is one drink daily for women and two for men.

Keep in mind that if you seem to get sick often, you are not necessarily unhealthy. Instead, you may be more susceptible to illnesses than others.

A Quick Review

Some people are simply more susceptible to getting sick than others. Lifestyle choices, environment, genetics, and age play key roles in determining immunity. Even if you cannot entirely control your immune system, fostering healthy habits might help protect you against infections.

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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