• Allergies are your body’s reaction to a normally harmless substance.⁵
• These substances are usually called allergens.
• If you have an allergy to a particular allergen, your body will overreact to its presence in your body.⁵ 
• Allergens can enter the body by the airways (breathing an allergen), skin (touching an allergen), gastrointestinal tract (ingesting an allergen) or by entering the circulatory system (allergen entering the bloodstream).⁶

Allergies can be classified as seasonal or perennial.

• Seasonal allergies are allergies that occurs during specific times of the year. 

  A seasonal allergy, often called allergic rhinitis or hay fever.⁷

• Perennial allergies are sometimes referred to as indoor allergies and are the cause of year-round allergies.