Tonsillitis is inflammation of the palatine tonsils, paired lymphoid tissues located at the sides of the throat that contribute to immune surveillance of material entering through the mouth and nose. It can be caused by viruses or bacteria and is common in children and adolescents, although adults can also develop it. Symptoms typically include sore throat, painful swallowing, swollen or inflamed tonsils and fever, with some people developing enlarged neck lymph nodes, headache or general malaise. The presence of tonsillar inflammation does not by itself identify the cause, because viral and bacterial infections can produce overlapping appearances. Tonsillitis may be an isolated episode or may recur repeatedly, and persistent or severe disease requires consideration of complications and alternative diagnoses.
Viral infections account for many cases of tonsillitis, particularly when symptoms occur alongside cough, runny nose, hoarseness or other features of a broader respiratory infection. Certain bacterial infections can also cause acute tonsillitis, with group A streptococcal infection being an important example because appropriate treatment can reduce certain complications and transmission. White or yellow material on the tonsils is not by itself proof of bacterial infection because exudate can occur in several infections. Similarly, the intensity of throat redness does not reliably distinguish causes. Clinical assessment may use combinations of symptoms and examination findings to estimate the likelihood of bacterial infection, followed by testing where appropriate according to local clinical practice.
Symptoms can vary from mild discomfort to severe throat pain that makes eating and drinking difficult. Inflamed tonsils may become enlarged and can contribute to a sensation of throat obstruction, while associated lymph-node inflammation can produce tender swelling in the neck. Some viral illnesses can produce particularly marked tonsillar enlargement or exudate and may be accompanied by profound fatigue or widespread lymph-node enlargement.
Tonsillitis should therefore be interpreted within the broader clinical picture rather than diagnosed solely from the appearance of the tonsils. Difficulty breathing, inability to swallow saliva, severe dehydration, rapidly progressive swelling or significant one-sided throat symptoms can indicate complications or another urgent condition and require prompt medical evaluation.
Investigation is usually guided by symptoms and examination. When bacterial infection is suspected, throat swabs or rapid testing may be used depending on the healthcare setting and local guidelines. Blood tests are not routinely necessary for straightforward acute tonsillitis but may be considered when systemic illness or a specific alternative diagnosis is suspected. Clinicians also consider whether symptoms are compatible with glandular fever or other viral infections, because management and counselling can differ. A recurrent pattern may prompt evaluation of the frequency, severity and functional consequences of episodes rather than repeated treatment of every sore throat without establishing whether the episodes represent true tonsillitis.
Treatment is primarily supportive for viral disease and can include adequate fluids, analgesia and measures that make swallowing more comfortable. Antibiotics may be appropriate when a bacterial cause is sufficiently likely or confirmed, with the choice determined by local prescribing guidance and individual circumstances. Antibiotics do not treat viral tonsillitis and should not be used simply because tonsils appear red or coated.
Recurrent tonsillitis can sometimes lead to consideration of surgical removal of the tonsils when episodes are sufficiently frequent or disabling and meet accepted clinical criteria. Tonsillectomy is a surgical procedure with potential benefits and risks, including postoperative pain and bleeding, so the decision depends on the documented burden of disease rather than on the existence of occasional sore throats.
Complications of tonsillitis are uncommon but clinically significant. A peritonsillar abscess can develop in the tissues beside a tonsil and typically causes severe unilateral throat pain, difficulty opening the mouth, altered voice and deviation of structures in the throat. Severe bacterial infection can also occasionally spread beyond the local tissues and produce systemic illness. Some streptococcal infections are associated with immune-mediated complications occurring after the acute infection, which is one reason appropriate diagnosis and treatment can matter in selected circumstances. Nevertheless, most episodes resolve without serious consequences. The practical challenge is identifying the small proportion with complications without subjecting the large number with self-limited viral infections to unnecessary investigations or antibiotics.
The term tonsillitis refers specifically to inflammation of the tonsils and should be distinguished from the broader symptom of sore throat, which can arise from pharyngitis, laryngeal disease, reflux, irritation or other causes. The tonsils themselves are part of lymphoid tissue associated with immune function, although their removal does not generally produce major immune deficiency because the immune system has many other components.
Historically, tonsillectomy was performed very frequently, but modern practice generally applies more selective criteria because surgery carries risks and not every recurrent throat infection is sufficiently attributable to tonsillitis to justify removal. A common misconception is that enlarged tonsils automatically require surgery; size alone is not the only determinant, and the clinical consequences are more important.
Tonsillitis is particularly significant in paediatric and adolescent medicine because repeated episodes can interfere with school attendance, sleep, eating and family routines. Prevention of respiratory infections through ordinary hygiene measures may reduce some episodes, although there is no universal method of preventing tonsillitis because multiple viruses and bacteria can cause it. People with persistent or recurrent symptoms may require assessment by primary-care or ear, nose and throat clinicians, particularly when episodes are severe or associated with obstructive symptoms. The condition illustrates the limitations of diagnosing infections from appearance alone: clinical findings overlap considerably, and decisions about testing and antibiotics need to account for the likely cause, severity and risk of complications.
