These microscopic creatures thrive in beds, pillows, and carpets, and their presence can worsen with prolonged indoor time. Washing bedding in hot water can help.

When you spend more time indoors, you have more exposure to pets. Frequent pet washing and keeping pets off furniture can help minimize dander exposure.

Mold can grow in damp indoor areas and is also present on outdoor leaves that can be tracked inside. Mold can also be brought inside on Christmas trees. 

While more associated with fall, strong winds can carry ragweed pollen into the winter, triggering allergy symptoms. 

In specific regions, these trees release pollen from December to February, leading to a condition sometimes called "cedar fever". Symptoms can mimic the flu, but without the fever. 

Thawing, damp environments and decaying fall leaves can release mold spores into the air.