Animal Allergy: Allergies Worse in Winter Make an Appointment Refer a Patient Ask a Question Reviewed by Sanny Chan, MD, PhD (November 01, 2016) Dogs and cats. They may be your best friends, but if you have allergies they could be your worst enemy, especially in the winter. As the weather gets colder and dogs and cats spend more time inside, the level of animal dander rises in the home. There are two major concerns: It's cold and the house is closed up. There's less fresh air coming into the house. Downside of Energy Efficiency Because new houses are built to a high level of energy efficiency and older homes are being updated, the amount of outside air exchanged with inside air is dropping dramatically in homes throughout the United States. Although this is energy efficient, the downside is that you're breathing the same air over and over, and allergens build up in the house. Replace Furnace Filter A forced-air furnace also can increase problems because it circulates dander-laden air throughout the home. Changing the furnace air filter regularly and closing the vent and door can help relieve allergy symptoms. Making a secondary filter from a piece of muslin or cheesecloth and taping it to the inside of the vent in a room also may remove some allergens. Clean Humidifiers Heated air also creates a considerable drop in humidity in the home so many people use humidifiers, which can be a breeding ground for mold growth. People using humidifiers during the winter should clean them weekly with a solution of bleach and water to kill mold. Never allow humidity in the home to rise above 40 percent. At higher concentrations, dust mites, which cause allergies, begin to thrive and the possibility of mold contamination increases dramatically. Reduce Exposure Evidence shows that allergy and asthma symptoms may improve over time if the recommended environmental control changes are made. Environmental control means to make changes in your environment (home, workplace, etc) to reduce exposure to certain allergens. Many environmental controls are for the entire home, but the bedroom is the most important because it is where people usually spend a third to half of their time. Learn ways to reduce exposure to animal allergens even if you own a pet. View Allergy Home Animal Allergy: Reduce Exposure Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.