Rhinitis, sinusitis, pharyngitis and tonsillitis

Lesion

Viruses and allergens inflame the nose and throat. Repeated attacks cause polyps, blocked sinuses and bacterial infection.

Updated Nov 12, 2026

Key points

Common cold: rhinoviruses, adenoviruses, coronaviruses; edematous red mucosa with profuse catarrhal discharge.
Allergic rhinitis: IgE-mediated early and late phase; eosinophil-rich infiltrate; associated with asthma and eczema.
Nasal polyps: edematous stroma with eosinophils, glands and plasma cells; with aspirin-exacerbated respiratory disease (asthma, polyps, NSAID sensitivity) and cystic fibrosis (polyps in a child suggest CF).
Sinusitis: usually after rhinitis; maxillary sinusitis can come from a dental (periapical) infection; obstructed frontal sinus can form a mucocele.
Mucormycosis of the sinuses in diabetic ketoacidosis or neutropenia: invasive, destructive, can reach the orbit and brain.
Group A streptococcal pharyngitis can lead to rheumatic fever and post-streptococcal glomerulonephritis.

What it is

The upper airway is the commonest site of infection and allergy. Infectious rhinitis (the common cold) is viral; allergic rhinitis is a type I hypersensitivity. Repeated inflammation produces nasal polyps and chronic rhinitis, and blocked drainage leads to sinusitis. Pharyngitis and tonsillitis are mostly viral, with group A Streptococcus the important bacterial cause.

Structure

Rhinitis: mucosal edema, vascular congestion, mononuclear or eosinophilic infiltrate; mucus overproduction.
Nasal polyp: smooth, grey, gelatinous mass; loose edematous stroma, hyperplastic or cystic glands, eosinophils, neutrophils and plasma cells.
Chronic sinusitis: thickened mucosa, chronic inflammation, sometimes squamous metaplasia and fibrosis.
Tonsillitis: reactive follicular hyperplasia, crypt abscesses with neutrophils and exudate.

Step by step

Viruses or allergens trigger edema and mucus in the nasal mucosa.
Swollen mucosa blocks the sinus ostia and Eustachian tubes.
Trapped secretions are invaded by bacteria from the nasopharynx or mouth: acute sinusitis or otitis.
Repeated inflammation makes the mucosa protrude into the cavity (polyps), further blocking drainage.
Persistent obstruction leads to chronic sinusitis; in impaired hosts fungi invade.

Upper airway inflammation

Condition	Main cause	Key lesion
Allergic rhinitis	IgE to pollen, dust mites, dander	Edema with eosinophils
Nasal polyps	Recurrent rhinitis, AERD, cystic fibrosis	Edematous stroma, eosinophils
Acute sinusitis	Viral then bacterial (oral and nasal flora)	Mucosal edema, pus in sinus
Streptococcal pharyngitis	Group A Streptococcus	Exudative tonsillitis, crypt abscesses
Peritonsillar abscess	Spread of tonsillitis	Pus between tonsil capsule and constrictor

Clinical notes

Most upper respiratory infections are viral and resolve without antibiotics.
Polyps cause nasal obstruction and loss of smell; recurrent polyps in a child prompt a sweat test for CF.
Peritonsillar abscess is a complication of tonsillitis needing drainage.

Test yourself

Think of the answer, then tap the question to see it.

What disease should nasal polyps in a child suggest?

Cystic fibrosis.

What is aspirin-exacerbated respiratory disease?

The triad of asthma, nasal polyps and sensitivity to aspirin and other NSAIDs, driven by excess leukotrienes.

Which fungal sinus infection is a threat in diabetic ketoacidosis?

Mucormycosis, which invades vessels and can spread from the sinuses to the orbit and brain.

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Connections

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Allergic Rhinitis (StatPearls (NCBI Bookshelf), 2025); Acute Sinusitis (StatPearls (NCBI Bookshelf), 2025); Streptococcal Pharyngitis (StatPearls (NCBI Bookshelf), 2025).

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