Among the most common causes of a sore throat and phlegm are colds and other viruses, though bacterial infections may cause these symptoms as well. In other cases, allergies are at the root of such symptoms, and lifestyle choices such as smoking cigarettes may also lead to them as well. A person may even develop these symptoms after being exposed to secondhand smoke.
The common cold often causes a sore throat, stuffy nose and phlegm. A sore throat is often one of the first indications that a person has a cold, and phlegm frequently develops later in the course of the illness. Some people assume that phlegm means a bacterial infection, especially if the phlegm is discolored rather than clear. In reality, however, discolored phlegm can also develop as the result of the cold virus.
Other viruses may cause a sore throat and phlegm as well. A sore throat is one of the common symptoms of a case of influenza, for example, and it's often accompanied by a dry cough that does not produce much or any phlegm. Later in the illness, however, a person may start to notice phlegm as well. Additionally, both of these symptoms may develop when a person has a flu-like illness rather than the flu.
An individual may also develop these symptoms due to allergies that affect the respiratory system. Many people are aware that allergies can cause a person to feel a tickle in his throat or develop a cough, but the signs can mimic some of the symptoms of a common cold as well. In fact, a person with an allergy may sometimes have a sore throat that lasts longer than it would with a common cold. He may also develop a cough that produces phlegm whenever he has significant exposure to an allergen.
Sometimes, a sore throat and phlegm are unrelated to an illness, but develop because of something the affected person does. A prime example of this is the sore throat and coughing that may accompany cigarette smoking for some people. Smoking can irritate the smoker’s respiratory passages and lead to the development of phlegm as well. This may be worse if the individual also has a cold or allergies. Additionally, some people may develop these symptoms when they are exposed to secondhand smoke.