Animal users who have asthma or allergic conditions may become sensitive to animal allergens with repeated exposure. Up to 20% of allergic animal users may develop occupational asthma, which can limit the ability to work and may lead to permanent disability. An allergy is the over-reaction response of your immune system to substances in the environment. These substances are called allergens and can cause sneezing, watery and itchy eyes, itchy skin, sinus or nasal congestion or more serious reactions. When we touch or work around animals, we expose our bodies to these allergens.