The tonsils are oval-shaped masses of lymphatic tissue situated on each side at the back of the throat. They are part of the body’s lymphatic system, acting as an initial defense mechanism against inhaled or ingested pathogens like bacteria and viruses. When the tonsils encounter an infection, they become inflamed, a condition known as tonsillitis. Unilateral swelling, where only one tonsil appears enlarged, is a noticeable departure from the body’s typical bilateral immune response and often causes concern.
Common Asymmetrical Infections
The difference in size between the two tonsils is frequently the result of a common infection, where swelling is simply more pronounced on one side. This asymmetry occurs with common viral infections, such as the common cold, or bacterial infections like Streptococcal pharyngitis (strep throat). The immune system’s localized reaction may be stronger or faster in one tonsil compared to the other.
A person may only perceive the swelling as unilateral, especially in the early stages of an illness, because pain or discomfort is felt more intensely on one side. In these cases, the inflammation is usually short-lived, with symptoms like fever and sore throat resolving within a few days, and the tonsil size returning to normal. The body’s varied response means that one tonsil may be reacting more aggressively to the infectious agent.
When a Localized Abscess Develops
A more serious cause of unilateral swelling is the development of a peritonsillar abscess, sometimes known as Quinsy. This condition is a complication of tonsillitis where pus collects in the tissue space next to one tonsil, pushing the affected tonsil toward the center of the throat. This pus-filled collection causes severe, observable swelling that is almost always limited to one side.
The symptoms accompanying an abscess are specific and help differentiate it from standard tonsillitis. Patients typically experience trismus, which is difficulty opening the mouth fully. The abscess also causes a significant, constant, and often excruciating sore throat, along with a muffled or “hot potato” voice quality. This condition is urgent because the swelling can obstruct the airway, demanding immediate medical attention.
Atypical Diseases and Non-Infectious Causes
Systemic infections can lead to severe, sometimes asymmetrical, tonsillar enlargement, notably infectious mononucleosis, caused by the Epstein-Barr virus. Mononucleosis often results in widespread lymphadenopathy and can cause one tonsil to swell more significantly than the other, sometimes accompanied by a gray-white coating. The severity and duration of this swelling set it apart from typical viral tonsillitis.
Not all unilateral tonsil enlargement is related to an active infection, as it can be due to structural or neoplastic changes. Benign conditions like tonsillar hyperplasia or a cyst can cause one side to appear bigger than the other without symptoms. In rare instances, persistent, unexplained unilateral swelling can be a sign of malignancy, such as tonsillar carcinoma or lymphoma. An adult with asymptomatic, increasing unilateral enlargement warrants diagnostic testing to rule out cancer, especially if other signs like a neck lump or unexplained weight loss are present.
Key Symptoms Requiring Immediate Medical Care
Unilateral tonsil swelling accompanied by certain severe symptoms should prompt immediate consultation with a healthcare provider. Difficulty breathing or noisy breathing (stertor) indicates potential airway compromise, especially when a peritonsillar abscess is suspected. The inability to swallow even saliva, often resulting in drooling, or intense pain that prevents drinking are serious indicators of severe obstruction or infection.
Patients should seek medical evaluation if a high fever does not decrease with over-the-counter medication or if swelling and pain persist for more than 48 hours without improvement. The presence of trismus, or difficulty opening the mouth, specifically points toward the need for urgent assessment for an abscess. Severe functional impairment accompanying unilateral tonsil swelling should never be disregarded due to the risk of complications, including airway obstruction.