What causes swelling and pain on the left side of the throat?

Swelling and pain on the left side of the throat may result from factors such as a pharyngeal foreign body, tonsillitis, or acute pharyngitis.

1. Pharyngeal Foreign Body

Swelling and pain on the left side of the throat may be caused by a foreign body lodged in the pharynx—for example, accidentally swallowing hard objects such as chicken bones or fish bones, which become stuck in the pharynx or at the esophageal inlet.

2. Tonsillitis

This symptom may also indicate tonsillitis, typically caused by bacterial or viral infection. The left tonsil may become congested and swollen; in severe cases, acute suppurative tonsillitis may develop, leading to swelling and pain on the left side of the throat.

3. Acute Pharyngitis

Acute pharyngitis can likewise cause swelling and pain on the left side of the throat. It is commonly triggered by bacterial or viral infections—including *Streptococcus pyogenes* (Group A β-hemolytic streptococcus), influenza virus, or Epstein–Barr virus—which induce inflammatory irritation of the pharyngeal mucosa. When inflammation resulting from infection affects the left pharyngeal wall, these symptoms may occur.