Pet allergy is an allergic reaction to proteins found in an animals skin cells, saliva or urine. Signs of pet allergy include those common to hay fever, such as sneezing and runny nose. Some people may also experience signs of asthma, such as wheezing and difficulty breathing. Dogs have a global distribution and all dogs produce allergens. Allergic sensitization to dogs is considered to be a risk factor for asthma and rhinitis, and has increased significantly over recent decades for both children and adults. Dog allergen particles are tiny so they easily become airborne, disperse effectively, and can enter small bronchioles to reach lower airways. Dog hair and dander extracts contain many antigens, any of which can bind to IgE antibodies and trigger respiratory symptoms in sensitized individuals.