Allergies are not limited to the summer and spring months. Many people will suffer from allergies in the winter, the symptoms of which are nasal congestion, runny noses, sneezing, and all the other uncomfortable symptoms that accompany inflammation-causing reactions to allergens. So, while it is true that seasonal allergies tend to improve for most people during winter, not everyone enjoys such a reprieve from the discomforts of allergies during the cooler months.
Winter results in people spending more time indoors; this in turn increases their exposure the allergens that are found inside the house, such as mold, dust mites and pets (who also spend more time inside during the cold season).
In addition, many mistake the increased incidences of runny noses and coughing during the winter months for the flu. Flu symptoms mirror allergy symptoms, which are actually caused by the inflammatory effects of histamine that is produced by the body when exposed to foreign substances that it doesn't recognize, such as germs or allergens. However, flu symptoms should disappear within a short time; when these symptoms fail to resolve, winter allergies should be considered.