1.    Allergies, cold air, physical and chemical damage.
2.    Alpha-1 agonists .eg Ephedrine. Antihistamines and antimuscasrinic drugs.eg Diphenhydramine. Corticosteroids(budesonide), Mast cell stabilizers(ketotifen), Mucolytics(mesna), volatile oils.
3.    Decongestants may be selective or direct-acting and non-selective adrenergic agonists. They range from short-acting drugs (4-6 hours), intermediary-acting (8-10hours) and long-acting (12 hours). They are normally administered topically as nasal sprays, drops or gels. 
4.    Rhinitis medicamentosa or privinism is a condition caused by long term use of decongestants, where nasal blood vessels are irreversibly constricted and the adrenergic receptors are unresponsive. It is treated by stopping the use of alpha-1 agonists and temporarily using corticoid therapy.
5.    First generation antihistamines are competing antagonists on the H1 receptor and also have antimuscarinic effects. Second generation anihistamines are not however not multipotent ant are only useful in allergic rhinitis, for long term and short term.
6.    Corticosteroids are valid in non-infection conditions and administered topically. Anti-allergy drugs are only useful in allergic rhinitis and are administered . Mesna is a mucolytic and is administered topically. Normal saline solution is first choice for children and pregnant women and is administered topically.