Chilly air means sniffly noses. When we breathe in, our noses warm the air and add moisture to it as it travels down into our lungs. Cold, dry air irritates your nasal lining, and as a result, your nasal glands produce excess mucus to keep the lining moist. That can cause those big, heavy drops that drip from your nostrils. Wearing a scarf in cold weather can help, because the air warms before it hits your nose.