What are the categories of medications used in the treatment of allergic rhinitis and how do they differ in their mechanisms?

Antihistamines are often used as first-line medications to treat mild allergic rhinitis and are currently the most prescribed treatment for allergic rhinitis.
Antihistamines block the H1 receptor and act by competing with histamine for H1 receptors on cells.
Antihistamines of the first generation are lipophilic, cross the blood-brain barrier, and produce sedation. They have a shorter duration of action and anticholinergic effects, but have the same efficacy as second-generation antihistamines.
Second-generation antihistamines are preferred by most allergists because they are generally less sedating and do not interfere with school or work performance compared to first-generation antihistamines.
Intranasal corticosteroids are very effective in the treatment of allergic rhinitis and have been shown to reduce nasal symptoms of itching, sneezing, runny nose, and congestion compared to placebo.