Much of the nation is experiencing large fluctuations in temperatures this week, with unseasonable highs, followed by drops of up to 40 degrees in 24 hours. Experts say that these fluctuations can make you more susceptible to getting sick. The popular saying, being “under the weather” isn’t just a catchy phrase. Many people get legitimately sick when the seasons change, or the temperature and barometric pressure significantly fluctuate.

According to Dr. Michael Kaplan, of Kaplan Sinus Relief, some of the ways your body reacts to changing weather include:

• Sinus and joint pressure.

• Swollen tissues.

• Narrowed blood vessels.

• Migraines or headaches.

• Dried, cracked mucus membranes.

• Weakened immunity.

“The change in temperature doesn’t make you sick but changes in weather conditions can predispose you to getting sick,” says Dr. Neha Vyas, a family medicine expert at the Cleveland Clinic. There are three main factors that accelerate the rates of illness during these weather changes:

• Drier air. “Winter means colder, drier air that dries out the mucus membranes and that allows viruses into your body quicker,” Vyas says. “Cracks in the mucous membranes can allow those viruses to settle and access your body.”

• The cold. Colder air weakens our immune system, says the expert, making us more susceptible to infections.

• Exposure. During the colder months we are also indoors more often exposing us to other people in close quarters. Winter is also the peak period for certain viruses, particularly influenza, that typically don’t survive as well in summer.

The sudden fluctuations in weather patterns that we are seeing across the country, also contribute to illness, according to experts at Piedmont healthcare systems.

“Changes in weather are basically challenges to our immune system and to our musculoskeletal system,” explains Dr. Vikash Modi, a family medicine physician. “Our bodies get used to a certain climate, and when those things change suddenly, our body has to try to adapt. Unfortunately, sometimes our bodies have a difficult time adjusting, which can trigger an illness.”

Here are six health conditions that can be triggered by a sudden change in the weather:

1. Infection and illnesses of the upper respiratory tract. Modi says this is due to improper clothing. When weather fluctuates quickly, we often dress in too many layers or not enough layers, so the body gets overheated or too cold. This can affect immune response and trigger upper respiratory infections.

2. Chronic sinus and throat issues. Heating and air systems struggle to keep up with fluctuating temperatures so alternating heating and cooling systems cause drier air. Dehumidified air is the perfect storm for severe and chronic sinus and throat issues. Change air filters every six months, says Modi.

3. Seasonal asthma and bronchitis are often caused by cold air. People who have these conditions should use an inhaler seasonally to avoid severe and chronic coughing episodes.

4. Seasonal allergies from pollen. Plants also get confused by changing weather patterns, says Modi. “This means flowers bloom early and release pollen which can aggravate people with seasonal allergies.”

5. Cold and flu outbreaks. When the weather temporarily gets better, people gather for group activities, increasing the risk of illness. “When large groups gather, we all need to be more careful of hand hygiene and covering our mouths and noses while coughing and sneezing,” says Modi.

6. Muscle and joint injuries. When the weather suddenly gets warmer, people tend to leap into outdoor activities. But being extremely demanding on muscles and joints that have been inactive during cooler spells can lead to injuries.