Types of Allergic Reactions   Classified according to their causes and symptoms, there are 9 major types of allergic reactions:   Hay fever (allergic rhinitis) - caused by exposure to airborne allergens in the nose, such as dust mite feces, mould spores, pollen grains, cockroach excrement, and animal dander.   Conjunctivitis - occurs when the airborne allergens cause inflammation of the inside lining of the eyelids   Asthma - the patient experiences difficulty in breathing due to obstruction in the airways, usually with excessive mucus production and swelling / inflammation of the airways.   Sinusitis - it is an infection of the sinus areas of the skull, which are between the eyes, on either side of the cheeks, in the forehead, and in the centre of the head behind the nasal cavity.   Dermatologic allergies - allergic skin diseases caused by a wide range of allergens.   Allergic drug reactions - adverse allergic reactions to drugs / medicines used to treat other illnesses.   Chemical photosensitivity - it involves an increase in sensitivity of human bodies to sunlight and other types of ultraviolet light due to some medications.   Occupational / environmental allergies - allergic problems causes by industrial materials or chemicals used in the patient's job, home or other environments.   Allergic emergencies (anaphylaxis) - it is a very serious manifestation of the allergic response that may become life-threatening if not treated immediately and properly.