Most sore throats are caused by viruses — the same germs that cause colds and flu (influenza). Less often, sore throats are due to bacterial infections. Viruses and bacteria both enter your body through your mouth or nose — either because you breathe in particles that are released into the air when someone coughs or sneezes, or because you have contact with an infected person or use shared objects such as utensils, towels, toys, doorknobs or a telephone. Because the germs that cause sore throats are contagious, they can spread easily wherever large numbers of people congregate, such as schools, child care centers and offices.
The most common viral illnesses that cause a sore throat include:
• Common cold
• Flu (influenza)
• Mononucleosis (mono)
Other viral illnesses that can cause a sore throat include:
• Croup — a common childhood illness characterized by a harsh, barking cough
Bacterial infections that can cause a sore throat include:
• Strep throat
• Diphtheria — a serious respiratory illness that's rare in industrialized nations but is more common in developing countries
Other causes of sore throat include:
• Allergies. The same pet dander, molds and pollens that trigger allergic reactions such as red, swollen eyes and a runny nose can also cause a sore throat.
• Dryness. Dry indoor air, especially in winter when rooms tend to be overheated, can make your throat feel rough and scratchy, particularly in the morning when you first wake up. Breathing through your mouth — often because of chronic nasal congestion — also can cause a dry, sore throat.
• Pollution and other irritants. Outdoor air pollution can cause ongoing throat irritation. But indoor pollution — especially tobacco smoke — is an even greater cause of chronic sore throat. Smokeless tobacco, alcohol and spicy foods can also inflame your throat.
• Muscle strain. You can strain muscles in your throat just as you can strain them in your arms or legs. If you've ever gotten a sore throat after yelling at a concert or sporting event, you've likely strained your throat muscles. Your voice may also be hoarse (a symptom of laryngitis).
• Acid gastroesophageal reflux disease (GERD). This occurs when stomach acid backs up into your food pipe (esophagus). Normally, a circular band of muscle (lower esophageal sphincter) blocks acid from coming up into the esophagus. But if the sphincter relaxes abnormally or weakens, stomach acid can back up, irritating your throat as well as your esophagus. Throat irritation caused by GERD doesn't occur with other symptoms of a viral illness, and it tends to be persistent, rather than lasting just a few days. It's also far more common in adults than in children. In many cases, you can prevent or reduce acid reflux with simple lifestyle changes — losing weight, avoiding foods that cause you discomfort and not eating right before bed, for example. When these aren't effective, over-the-counter or prescription medications may offer some relief.
• HIV infection. HIV-positive people sometimes develop a chronic sore throat. This is due to a secondary infection such as oral thrush or cytomegalovirus, a common viral infection that can be extremely serious in people with compromised immune systems.
• Tumors. If you smoke or abuse alcohol, you're at high risk of tumors of the throat, tongue and voice box. In some people these tumors cause few, if any, signs and symptoms. In others, they can lead to hoarseness, difficulty swallowing and sore throat.