The tonsils are lymphatic tissues located at the back of the throat, part of the body’s immune system, defending against pathogens entering through the mouth and nose. While tonsils typically appear symmetrical, it can be concerning when only one tonsil becomes noticeably swollen. This unilateral swelling can indicate various underlying conditions, ranging from common infections to more serious issues.
Common Infectious Causes
Infections are frequent culprits behind tonsil swelling, and while tonsillitis often affects both tonsils, sometimes one side may appear more enlarged or inflamed. Bacterial infections, such as those caused by Streptococcus pyogenes (strep throat), can lead to tonsillitis, causing inflammation. Although usually bilateral, a localized response or the stage of infection might make swelling more prominent on one side. Viral infections, including those responsible for the common cold, influenza, or infectious mononucleosis (Epstein-Barr virus), can also cause tonsil inflammation. Mononucleosis, in particular, can result in significantly swollen tonsils, and occasionally, the swelling might be more pronounced on one side. These infections typically present with additional symptoms like a sore throat, fever, difficulty swallowing, and general malaise.
Peritonsillar Abscess
A peritonsillar abscess (PTA), also known as quinsy, is a collection of pus behind one tonsil. This condition typically develops as a complication of bacterial tonsillitis when the infection spreads into the soft tissues surrounding the tonsil, creating a pus-filled pocket. The unilateral nature of the abscess means it almost always causes significant swelling on only one side of the throat.
Individuals with a peritonsillar abscess often experience severe, unilateral throat pain, which can be worse on the affected side. Other distinct symptoms include difficulty opening the mouth widely (trismus), a muffled or “hot potato” voice, and pain when swallowing, sometimes leading to drooling. Ear pain on the same side as the abscess and fever are also common. This condition requires prompt medical attention to prevent the infection from spreading further or blocking the airway.
Less Common Causes
Beyond common infections and abscesses, other less frequent conditions can lead to unilateral tonsil swelling.
Benign Growths and Cysts
Benign growths or cysts can develop on or near a tonsil. These growths, such as tonsillar retention cysts, often grow slowly and may not cause symptoms unless they become large enough to create a sensation of something being stuck in the throat or difficulty swallowing.
Tonsil Stones and Irritation
Tonsil stones, or tonsilloliths, are small, hardened deposits of debris, bacteria, and calcified material that form in the tonsil’s crevices. While usually small, larger or impacted stones can lead to irritation, inflammation, and localized swelling, potentially causing discomfort or bad breath. Direct trauma to the tonsil, perhaps from a sharp food item, or chronic irritation from conditions like persistent acid reflux, could also cause temporary or localized inflammation and swelling.
Malignancy
Though rare, malignancy, such as tonsil cancer (often squamous cell carcinoma or lymphoma), can also present as unilateral tonsil enlargement. This is a more serious cause, particularly in older individuals or those with specific risk factors like human papillomavirus (HPV) infection. Unilateral tonsil enlargement, especially if persistent, painless, or accompanied by an enlarged lymph node in the neck, warrants careful evaluation to rule out cancer.
When to Seek Medical Attention
Any persistent or worsening unilateral tonsil swelling should prompt a medical evaluation. Certain “red flag” symptoms necessitate immediate medical attention. These urgent symptoms include severe difficulty swallowing or breathing, which could indicate airway obstruction. Intense throat pain, particularly if it is worse on one side or makes opening the mouth difficult, is a concerning sign. A muffled voice, high fever, or if the swelling does not show any improvement within a few days, are also reasons to seek prompt medical advice.
The Diagnostic Process
When evaluating unilateral tonsil swelling, a healthcare provider will typically begin by taking a detailed medical history, asking about symptoms, their duration, and any associated conditions. This is followed by a physical examination, where the doctor will visually inspect the throat, including the tonsils, and gently feel the neck for swollen lymph nodes. This initial assessment helps narrow down potential causes.
A throat swab might be performed to test for bacterial infections like strep throat, with results sometimes available quickly or sent to a lab for more definitive testing. In cases where an abscess is suspected, imaging studies such as a CT scan may be used to confirm the presence of pus collection or rule out other masses. For suspected malignancy, a biopsy of the enlarged tonsil tissue would be performed to examine cells under a microscope. The specific diagnostic approach is tailored to the individual’s symptoms and the suspected underlying cause.