Does cold weather make you sick? For centuries, this myth has led grandmothers to insist that kids sit away from drafts, keep a hat on in cold weather, and avoid going outside with wet hair.

But if this is a myth, why do colds and the flu peak in the winter? The answers are complex and fascinating.

In terms of infectious illnesses, germs make you sick, not cold weather itself. You have to come in contact with rhinoviruses to catch a cold. And you need to be infected with influenza viruses to contract the flu.

Rhinoviruses peak in spring and fall, and influenza viruses peak in winter.

While the cold can’t be the only reason, there is a connection between being chilled and getting sick: cold air may contribute to conditions that lead to illness.

Viruses and the immune system

Some viruses are actually more likely to spread during cold weather. Rhinovirus (the cause of the common cold) replicates better at cooler temperatures, such as those found in the nose (33° to 35° Celsius) compared to the body core temperature (33° to 37° Celsius).

However, one study found that immune system cells initiate a more robust antiviral defense at lung temperature versus nasal cavity temperature. This might mean that the body may not fight the virus as well if the temperature in the nose and upper airway is lowered by environmental cold.

Some studies assert that influenza virus is most stable in cool, dry temperatures. However, other studies show that the disease is also prevalent in humid, warm climates. Other factors suggested as potentially affecting immune response include sudden changes in temperature or the impact of dark and light cycles.

But the bottom line is that cold doesn’t cause illness, although weather or other factors may weaken your ability to fight off illness.

Cold air forces you inside where it’s warm. Dry air associated with central heating makes it easy for cold and flu viruses to get into your dry nasal passages.

But thoughts on whether this theory is correct are divided.

Dry indoor air itself doesn’t get you sick. But it may play a role in letting aerosol droplets from a sneeze survive and prosper.

Researchers at Tianjin University in China found that students in dorm rooms with poor ventilation caught more colds.

Additionally, researchers at Virginia Tech found that good ventilation, as well as high relative humidity indoors, renders the influenza A virus inactive.

Dry air outdoors, as measured by absolute humidity, may also be linked to flu outbreaks. According to the National Institutes of Health (NIH), dry winter air allows the flu virus to survive and transmit itself.

Additional NIH research suggests that the coating of a flu virus becomes tougher at temperatures close to freezing, making them more active, more resilient, and easier to transmit in the winter.

It’s likely that being outside in cold weather inhibits the ability of mucus and nasal hairs to work disease agents out of your nose.

It’s also likely that when you get back inside in a room with the windows shut and people sniffling, you are more likely to be exposed to germs.

As people return to college, school, work, and day care in the fall, viruses find ideal conditions to hop from one host to another, before cold weather even sets in.

Hypothermia is an emergency that requires immediate medical care. This condition occurs when your body loses too much heat. It can result from exposure to extremely cold weather and elements.

Exposure to cold temperatures can cause hikers, the homeless, the very young, and the very old to begin to shiver, become confused, and even lose consciousness.

If you are in cold weather and encounter any of the following conditions, you’ll quickly face a medical emergency:

  • being exposed to a lot of wind or rain
  • becoming sweat-soaked
  • being submerged in water

If your body loses too much heat, get warm and get help.

If you like to run but have a history of asthma or upper respiratory conditions, cold weather can create problems. Warm up gradually before hitting your full stride outdoors and wear a neck gaiter over your mouth to help warm the air going into your lungs.

Also plan your route so you avoid likely triggers for your asthma, like leaf burning or chimney smoke.

People who truly believe cold weather causes infectious sicknesses may not understand how germs affect the body. While it’s important to protect against extreme temperatures for other reasons, they’re not the cause of illness.

Research at George Washington University found that young children are more likely to believe that cold weather causes illness. This means that children may not understand the best way to prevent getting sick from colds and the flu.

Knowing how germs work can help health educators teach effective prevention of colds and the flu, such as promoting good hand hygiene.