Ever wonder why some people seem to catch every cold that goes around, while others breeze through flu season untouched? The answer isn’t simple.

“There are so many things that go into it,” says Megan Cundiff, a physician assistant at Tidelands Health Family Medicine at Garden City.

Let’s break it down.

The adage that “you are what you eat” is a good reminder of how our diet can impact our health: eating fresh, healthy food keeps us healthy.

On the other hand, eating junk food like potato chips, cupcakes and candy can negatively impact your health by depriving your body and your immune system of the essential nutrients it needs to stay strong and healthy.

“It just raises the inflammation in your body without any health benefits,” Cundiff says. “Foods with little nutritional value make you feel run down and tired, and they make it harder for your body to fight infections.”

One key nutrient to watch? Vitamin D. Low levels of vitamin D are linked to a higher risk of respiratory infections, according to a PubMed study. The study found vitamin D may help calm inflammation in the lungs while also boosting the body’s natural defenses against germs that cause respiratory infections.

Cundiff adds that staying hydrated also impacts our health.

Stress doesn’t just mess with your mood; it can also mess with your immune system. When you’re stressed, your body releases cortisol, a hormone that suppresses white blood cells and increases inflammation.

“Your body’s trying to help you through fight-or-flight, but it ends up hurting you more,” Cundiff says.

One effective way to manage stress is to prioritize your sleep. The two are intimately connected.

“Adequate sleep can help with stress management because if you’re not sleeping well, you’re more likely to have high levels of cortisol,” Cundiff says. “If you’re not sleeping enough, your body can’t make enough of those disease-fighting cells.”

Sleep apnea can also disrupt your sleep. If you’re constantly tired, it might be worth checking for sleep disorders.

Exercise is a powerful immune booster. It helps manage stress, improves sleep and increases circulation of white blood cells and antioxidants.

“Exercise releases endorphins that are good for your overall health and reduces stress,” Cundiff says.

When your muscles move, they help push lymph, a clear fluid that carries nutrients and removes waste, through your body. This helps keep things flowing and prevents waste from building up when you’re not active.

Exercise can also relieve stress and improve sleep, which also boosts your immune system.

But that doesn’t mean you have to become a hardcore gym-goer to stay healthy. Studies show that 30 to 60 minutes of moderate aerobic activity, such as a brisk walk, a few days a week, is enough to get that benefit.

Handwashing is one of the simplest and most effective ways to stay healthy. We touch our faces about 23 times per hour, giving germs plenty of chances to enter our bodies.

“It’s good to wash your hands after coughing, sneezing or using the bathroom,” Cundiff says. “People touch their faces a lot more than they realize.”

Oral health can also play a role in boosting your immune system. Brushing your teeth removes bacteria and other microbes that can lead to infections. Your mouth is also connected to your nasal passages, which could allow illnesses to spread from one area to another.

Studies show that mouth infections can lay the foundation for more colds. Keeping your mouth’s microenvironment healthy can help keep your entire body healthy.

If you’re constantly feeling sick or tired, it may be time to take a closer look at your lifestyle or schedule an appointment with your health care provider.

Frequent illness could be a sign of an underlying issue like immunodeficiency, autoimmune disease, thyroid disorder and more.