Most throat infections are caused by viruses, the same ones responsible for the common cold and flu. Bacteria account for a smaller share, roughly 5 to 30% depending on age, and fungal infections are possible under certain conditions. Some non-infectious issues, like acid reflux, can also produce symptoms that feel identical to an infection. Understanding the different causes helps you figure out whether your sore throat will clear up on its own or needs treatment.
Viruses: The Most Common Cause
Viruses cause the majority of throat infections in both adults and children. The culprits are familiar: rhinovirus, adenovirus, influenza, and coronaviruses (including SARS-CoV-2). Most of these infections resolve on their own within a week.
Rhinovirus, the main driver of the common cold, is responsible for about 20% of pharyngitis cases. Interestingly, rhinovirus doesn’t actually invade the throat tissue itself. It infects the lining of the nose, causing swelling and increased mucus production that spreads irritation down into the throat. You catch it through airborne droplets or by touching contaminated surfaces and then touching your face.
Adenovirus works differently. It directly invades the throat lining, which is why adenovirus infections tend to produce more severe throat pain. In children, adenovirus can cause a distinctive combination of fever, sore throat, and pink eye known as pharyngoconjunctival fever.
Coronaviruses, including the one that causes COVID-19, are another frequent source. COVID-related sore throats can appear with or without other symptoms like cough, congestion, or fatigue. Standard cold-causing coronaviruses generally produce milder throat irritation as part of typical upper respiratory symptoms.
Infectious Mononucleosis
Epstein-Barr virus deserves its own mention because it causes infectious mononucleosis, commonly called “mono,” which produces a throat infection that’s noticeably more intense than a standard viral sore throat. It’s most common between ages 10 and 30.
In a study of 500 confirmed mono cases, at least 98% had sore throat, swollen lymph nodes, fever, and enlarged tonsils. About 85% had visible throat inflammation, and half had small red spots on the roof of the mouth. The distinguishing features of mono are significant fatigue, swollen lymph nodes in the back of the neck or armpits, and sometimes an enlarged spleen. A typical cold-related sore throat rarely produces this combination. Mono can take weeks or even months to fully resolve, making it one of the more disruptive viral throat infections.
Bacterial Infections
The most important bacterial cause is Group A Streptococcus, better known as strep throat. It accounts for 20 to 30% of sore throats in children and 5 to 15% in adults. Strep throat matters not because the infection itself is dramatically worse than a virus, but because untreated strep can lead to serious complications.
After exposure, it typically takes 2 to 5 days before symptoms appear. Strep throat tends to come on suddenly with a raw, painful throat, fever, and swollen lymph nodes in the neck. Cough and runny nose are usually absent, which can help distinguish it from a viral infection. The only way to confirm strep is through testing: a rapid antigen test (about 86% sensitive and 96% specific) or a throat culture, which is the gold standard. For children over 3, a negative rapid test is usually followed up with a culture to make sure strep isn’t missed, because untreated strep in this age group carries a real risk of acute rheumatic fever, a condition that can damage the heart.
Other possible complications of untreated strep include peritonsillar abscess (a pocket of pus that forms near the tonsil) and post-streptococcal kidney inflammation. These complications develop after the original infection resolves and result from the body’s immune response rather than the bacteria spreading directly.
Fusobacterium in Teens and Young Adults
A lesser-known bacterium called Fusobacterium necrophorum has gained attention as a cause of throat infections in adolescents and young adults. Some European studies have found it in roughly 10% of pharyngitis cases in this age group. While it often causes ordinary sore throats, it can occasionally lead to peritonsillar abscess or Lemierre syndrome, a rare but serious condition involving infected blood clots in the neck veins. Its clinical significance is still being studied, but it’s worth knowing about if you’re a young adult with an unusually severe or persistent sore throat.
Fungal Throat Infections
Oral thrush, caused by an overgrowth of Candida yeast, can extend into the throat and cause pain, difficulty swallowing, and white patches on the tongue or inner cheeks. Unlike viral and bacterial infections, thrush isn’t something you “catch” in the usual sense. The yeast already lives in your mouth in small amounts and only becomes a problem when something disrupts the balance.
Several factors raise your risk. Inhaled corticosteroids, commonly used for asthma, deposit medication in the throat that suppresses the local immune response and allows yeast to flourish. Rinsing your mouth after using an inhaler significantly reduces this risk. Antibiotics can also trigger thrush by wiping out the bacteria that normally keep yeast in check. Other risk factors include poorly controlled diabetes (high sugar levels in saliva feed the yeast), a weakened immune system from conditions like HIV or cancer treatment, wearing dentures, and chronic dry mouth. Babies and older adults are more susceptible due to naturally lower immunity.
Non-Infectious Causes That Mimic Infection
Not every sore, irritated throat is actually infected. Laryngopharyngeal reflux, or LPR, is a form of acid reflux where stomach acid travels past the esophagus and reaches the throat. Unlike typical heartburn, many people with LPR don’t feel burning in their chest at all, which is why it’s sometimes called “silent reflux.”
Your throat tissue is far more sensitive than your esophagus. It lacks the same protective lining and doesn’t have efficient mechanisms for washing acid away, so even small amounts of reflux can cause chronic soreness, hoarseness, a persistent feeling of something stuck in your throat, and frequent throat clearing. Over time, the acid also interferes with your throat’s ability to clear mucus and fight off actual infections, meaning LPR can indirectly make you more prone to upper respiratory infections.
Other non-infectious causes of throat irritation include allergies and postnasal drip, breathing dry air (especially overnight), smoking or exposure to secondhand smoke, and voice strain. These won’t produce fever or swollen lymph nodes, which can help you tell them apart from a true infection.
How to Tell What’s Causing Yours
A few patterns can help narrow down the cause. Viral throat infections usually come with cold symptoms: runny nose, cough, sneezing, and a gradual onset. Strep throat tends to hit abruptly with a high fever, no cough, and sometimes tiny red spots on the roof of the mouth. Mono brings extreme fatigue and widespread lymph node swelling that lasts for weeks. Thrush produces visible white patches. And LPR tends to be chronic, with hoarseness and throat clearing that’s worse in the morning.
The overlap between these conditions is real, though, and self-diagnosis is unreliable. A rapid strep test takes minutes and can rule in or out the one common cause that genuinely requires antibiotics. If your sore throat is severe, lasts more than a week, keeps coming back, or comes with difficulty breathing or swallowing, testing can clarify what you’re dealing with and whether treatment will help.