A sore throat is a common reason to see a doctor. Most of the time, it is a symptom of allergies, a cold, or the flu. While a sore throat can be painful, it is usually not serious.

However, when a throat is sore on only one side, it may be a sign of a different illness or condition.

In this article, we look at nine possible causes of a sore throat on one side. We also discuss when to see a doctor..

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Some illnesses and conditions cause soreness on only one side of the throat.

The body's lymph nodes act as filters, helping to identify and trap germs, such as viruses and bacteria, before they can infect other areas. As they do this, the lymph nodes may swell up and become sore.

The lymph nodes closest to the throat are on either side of the neck. These nodes can cause a feeling of soreness when they become swollen or inflamed.

Many illnesses and infections lead to swollen lymph nodes. Sometimes only one node in the area is sore, which can cause a sore throat on one side.

Some conditions that may lead to swollen lymph nodes include:

Many common viral illnesses, such as a cold or flu, can cause a sore throat. In these cases, the throat may only be sore on one side.

When the nose is congested, mucus and fluid drain down the back of the throat. This is known as postnasal drip. Continual drainage can irritate the throat, leading to a feeling of soreness or scratchiness.

A specific part of the throat may become more irritated by drainage. It may feel like one side is raw and inflamed.

Antibiotics cannot treat or weaken viral illnesses. If a cold, flu, or another viral illness is causing the sore throat, treatment will likely involve rest and fluids.

Tonsillitis describes inflammation of one or more tonsil. The tonsils are located at the back of the throat, and a virus or bacterium usually causes the infection and inflammation.

An infection in just one tonsil can cause pain on one side. It may also cause a fever, trouble swallowing, and noisy breathing.

Bacterial tonsillitis usually resolves with antibiotic treatment.

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A peritonsillar abscess requires immediate medical attention.

An abscess is a contained, pus-filled lump within tissue. It is usually caused by a bacterial infection.

A peritonsillar abscess forms in the tissues near the tonsils, usually when tonsillitis becomes severe or is left untreated. It may cause intense pain on one side of the throat. It may also cause fever, swollen lymph nodes, and trouble swallowing.

A person with a peritonsillar abscess requires urgent medical care. In severe cases, it can interfere with breathing.

The abscess may need to be drained by a doctor. Antibiotics are also used to treat the underlying infection.

Many things can injure the back of the mouth or throat, including:

  • burns from hot food or liquid
  • food with sharp edges, such as chips or crackers
  • endotracheal intubation, which is the insertion of a tube down the throat to help with breathing

If one side of the throat is sore from being scraped or burned, gargling with warm salt water may help to soothe symptoms.

Gastroesophageal reflux disease (GERD) is a condition that causes the stomach's contents, including stomach acid, to back up into the food pipe and throat.

GERD may be worse at night and when lying down. If stomach acid backs up when a person is lying on their side, it may lead to soreness on one side of the throat.

Other symptoms of GERD include:

  • pain or burning in the middle of the chest
  • the feeling of a lump or object in the throat
  • hoarseness
  • a dry cough
  • burning in the mouth

If GERD goes untreated for too long, it can damage the food pipe and throat. The condition is treatable with medications and lifestyle changes.

As the name implies, this viral illness usually causes sores to form on the hands, feet, and mouth. Sores can develop in the back of the mouth, near the sides of the throat, and one side may be more affected than the other.

Hand, foot, and mouth disease usually occurs in children under 5 years of age, but it can also spread to older children and adults.

The recommended treatment usually comprises rest, fluids, and over-the-counter medication for pain relief. However, the disease can cause dehydration, especially in young children. A person should see a doctor if they are unable to drink.

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Vocal therapy and resting the voice may help to treat vocal cord lesions.

Overusing or misusing the voice can lead to lesions or sores on the vocal cords. A lesion may form on one side, causing one area of the throat to be sore.

A person with a vocal cord lesion will usually notice a change in their voice, such as hoarseness.

These types of lesions are usually treatable. Resting the voice and vocal therapy are typically used to correct vocal cord lesions. In some cases, lesions will require surgery.

While they are among the least common causes of a sore throat, tumors can affect the throat and surrounding areas. They may be benign or cancerous.

A tumor can cause soreness on one side of the throat. It may be located in the back of the throat or tongue, or in the larynx, which is commonly known as the voice box.

Usually, a tumor will also lead to symptoms that do not occur with common infections and illnesses.

Possible additional symptoms include:

  • a lump in the neck
  • a hoarse voice
  • noisy breathing
  • unexplained weight loss
  • blood in the saliva or bloody phlegm
  • an ongoing cough

If a throat is sore on one side, the cause is usually a minor viral infection, such as the common cold. However, it is important to see a doctor if the following symptoms also appear:

  • an inability to eat or drink because of the sore throat
  • a severe sore throat that lasts for more than 7 days
  • swollen lymph nodes that get bigger as the sore throat feels better
  • difficulty breathing, or a feeling of the throat closing
  • trouble swallowing
  • a fever
  • pus in the back of the throat
  • body aches or joint pain
  • an earache
  • a rash
  • blood in the mouth
  • coughing up blood
  • a lump in the neck
  • a sore throat that goes away and comes back
  • hoarseness that lasts for more than 2 weeks

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