Adenoid hypertrophy is swollen lymph tissue in the upper airway between the nose and the back of the throat. Adenoid hypertrophy can result from both infectious and noninfectious causes. Viruses that are known to infect adenoid tissue include adenovirus, coronavirus, Epstein-Barr virus, and coxsackievirus. Common bacteria that do so include Streptococcus species, Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus. Gastroesophageal reflux disease (GERD), allergies, and cigarette smoke are noninfectious etiologies of adenoid hypertrophy.

Adenoid hypertrophy is far more common in children than in adults because the adenoids often naturally atrophy with age. The typical child with adenoid hypertrophy will be a mouth breather with a hyponasal-sounding voice. When the adenoids become large enough, they can cause obstructive symptoms. Common complications of adenoid hypertrophy include sleep problems such as snoring or obstructive sleep apnea (OSA), persistent rhinorrhea or nasal congestion, and frequent ear infections.