Forecasters have predicted the coming winter will be under the influence of El Niño. This climate pattern is expected to make the weather a bit milder and dryer for many parts of the country.

But that doesn’t mean special weather events like blizzards or polar vortexes are out of the forecast — those can still happen.

For some people, cold snaps are uncomfortable. But for people with cold-weather-triggering illnesses, cold weather can bring debilitating or even deadly diseases. 

Can Cold Weather Make You Sick?

Cold weather seems to bring on cold and flu season, however, there is evidence that cold weather can spark other illnesses. In a March 2022 study in Science of the Total Environment, researchers monitored an emergency department in Atlanta, where the temperature rarely drops below freezing. A week following a cold snap, visits to the emergency department for pneumonia or influenza increased by 11 percent, and hospitalizations increased by 8 percent. 

Why Does Cold Weather Make You Sick?

When the mercury drops, so does the body’s ability to fight off airborne viruses. And it’s not just the frigid temps that can make a person catch a cold. A lack of sunlight also plays a role. Shorter daylight hours and endless cloudy days can mean less vitamin D, which is needed to bolster the immune system.

Who Gets Sick in Cold Weather?

Certain groups might be more susceptible to cold-weather illnesses. Older adults tend to have a slower thermoregulatory mechanism, which means they may be more vulnerable after cold-weather exposure.

People with pre-existing conditions might also be at risk if the medications they are taking mask symptoms and prevent them from fully realizing the stress the cold weather is putting on their bodies. 

Read More: Why Do I Get Sick So Often, While Others Stay in Freakishly Good Health?

Rare Cold Weather Conditions   

Although colds or the flu are common conditions impacted by cold weather, some rare illnesses are triggered when the mercury drops. Diagnosing and treating these cold-weather-related conditions can be challenging for clinicians who have yet to encounter a case.

1. Cold Agglutinin Disease

This autoimmune disorder occurs when temperatures colder than 39 degrees prompt a person’s body to kill its own red blood cells.

Red blood cells typically have a 120-day lifespan before the body destroys them. When the body destroys red blood cells prematurely, the person can experience a range of symptoms, such as fatigue, anemia, dizziness, and heart palpitations. They might appear pale or jaundiced. Some may experience a rash.

Doctors can identify the disease by a blood test, and corticosteroids such as prednisone may be prescribed. This rare disease is typically only found in one out of one million people and develops when the person is between 40 and 80 years old.

2. Paroxysmal Cold Hemoglobinuria (PCH)

PCH is another autoimmune disease set off by cold weather, mainly affecting the hands and feet. With PCH, cold temperature prompts antibodies to attack red blood cells. The person might experience fatigue, joint pain, headache, nausea, and diarrhea. They also might be more vulnerable to respiratory infections. In advanced cases, the person might have cyanosis of their fingertips.

PCH diagnosis is possible through laboratory testing. The disease is rare, and symptoms appear in childhood for some people. PCH is also associated with viral and bacterial infections such as syphilis. If PCH is linked to another disease, treating the primary condition can provide a remedy. Other people might find relief with immune-suppressing medications. 

3. Cold Urticaria

For people with cold urticaria, a swim in cold water or exposure to frigid temperatures can initiate agony. Their skin develops painful, itchy welts. Some also experience anxiety, fatigue, headaches, and other symptoms.

Cold urticaria has two main types: acquired and familial. Acquired is more common, and there are several subtypes. Depending on the subtype, the person might experience a reaction to the cold almost immediately (as with primary acquired cold urticaria) or hours after the event (delayed cold urticaria)

Diagnosis can be as simple as applying an ice cube to the skin and watching for a reaction. Treatment may involve antihistamines with receptor blockers, but patients are generally advised to avoid cold water and to dress warmly on frigid days.

4. Keratolytic Winter Erythema (KWE)

This rare disease is seen more commonly in cold weather and causes the skin on a person’s soles and hands to turn red and blister. The skin then peels in a way that’s been described as so “substantial” that it can be “easily gripped.”

KWE is a relatively new disease that researchers first reported in South Africa in the 1970s. When experts analyzed the patients’ genealogical history, they realized they could all trace their lineage to a French ship captain from the 1700s.

Over time, KWE has been diagnosed in Denmark, Germany, Norway, and the U.S. To date, scientists have not been able to pinpoint an effective treatment.

Read More: Why We Feel So Terrible When We Get Sick