Indoor allergies are often the cause of year-round symptoms, which is why they are sometimes referred to as year-round allergies or perennial allergies. Indoor allergens are found indoors.⁸

Common indoor allergens include pets, mold, dust mites and cockroaches.⁵

A cold, is a viral illness that usually lasts for about a week and an allergy can persist for a long time. Allergies are not contagious, but the symptoms only vary slightly from the common cold, which is contagious.¹²

Animal dander is an allergen. Animal dander is loose skin cells (like dandruff) from animals such as dogs and cats. These skin cells, which contain secretions from glands in the animal's skin, float in the air, where they may be breathed in by people, resulting in symptoms of allergies.¹³

Allergic rhinitis (hay fever) is an allergic reaction to tiny particles in the air called allergens. When you breathe in allergens through your nose or mouth, your body reacts by releasing a natural chemical called histamine. Several indoor and outdoor allergens cause hay fever. Common causes include dust mites, mold, pet dander and pollen from trees and plants.

Symptoms of hay fever include sneezing, nasal congestion and irritation of the nose, throat, mouth and eyes. Allergic rhinitis is not the same as the common cold and it is not contagious.²

Antihistamines are commonly used to treat allergic rhinitis. These medications work by blocking the effects of histamine, a chemical released during allergic reactions that can cause irritating symptoms.¹⁶