There are many causes of post-nasal drip, or phlegm in the throat. They include:
Allergic rhinitis (hayfever)Non-allergic rhinitis (vasomotor rhinitis)SinusitisOveruse of nasal sprays such as AfrinHormonal causes such as pregnancy or hypothyroidism
Despite the variety of causes, the symptoms are similar (e.g., frequent need to clear the throat).
Allergic Rhinitis
Post-nasal drip may be a symptom of allergic rhinitis (hayfever), although it’s quite uncommon to have post-nasal drip as the only symptom. Typically, allergic rhinitis symptoms also include sneezing, nasal congestion, and a runny/itchy nose.
People with post-nasal drip caused by allergic rhinitis are diagnosed in much the same way as those with other symptoms.
Positive results on allergy testing suggest that there is an allergic cause to the symptoms. Having a good response to treatment with medicines for allergic rhinitis also increases the chance that post-nasal drip is related to hayfever.
Non-Allergic Rhinitis
Post-nasal drip may also be caused by non-allergic rhinitis, or vasomotor rhinitis. A non-allergic cause may be suspected in an older person with post-nasal drip symptoms who did not have problems with allergies when they were younger.
Non-allergic triggers of post-nasal drip may include:
Weather changes Exposure to strong odors or perfumes Eating spicy foods (gustatory rhinitis) Medicines for high blood pressure (medication-induced rhinitis) Exercise, sex (exercise-induced rhinitis)
By definition, people with non-allergic rhinitis show no reactions to allergy testing.
Treatments for non-allergic post-nasal drip include nasal steroids, nasal antihistamines, anticholinergic nasal sprays (such as ipratropium bromide) and older oral antihistamines, such as Benadryl (diphenhydramine) or Chlor-Trimeton (chlorpheniramine), used for their drying side effects.
Sinusitis
Post-nasal drip may also be the only symptom of sinusitis (infectious rhinitis), or it may go along with other symptoms, such as facial pain, nasal congestion, and colored nasal discharge.
When post-nasal drip is the only symptom of a sinus infection, it is usually because the infection is a low-grade infection that has been going on for months—and sometimes even years. Because the symptoms of these types of sinus infections are so mild, a diagnosis is often only made after a computed tomography (CT) scan is performed.
Post-nasal drip caused by a sinus infection is treated with antibiotics, although the antibiotics may need to be taken for a longer-than-typical period of time if the infection is thought to be chronic (lasting for more than two months or keeps coming back).
Rhinitis Medicamentosa
Rhinitis medicamentosa is a complicated way to describe the type of a runny nose and congestion that occurs when a person has been overusing a medication like Afrin (oxymetazoline).
As the body adapts the medication, more and more of the medication is needed. Severe post-nasal drip may occur until the cycle is broken.
Hormonal Causes
Pregnancy-induced rhinitis, or hormonal rhinitis, is a common cause of post-nasal drip in those who are pregnant.
Symptoms usually begin during the second trimester and persist until delivery, resolving shortly after the baby is born.
For others, hormonal rhinitis may occur with the use of birth control pills or when thyroid function is low (hypothyroidism.)
A Word From Verywell
There are many causes of post-nasal drip. Some of them may be identified after reviewing your history, such as your symptoms, response to treatments tried, and when your postnasal drip occurs. An examination of the consistency of the drainage (thinner with allergic and non-allergic rhinitis, thicker with sinusitis) can also be revealing.
While you may have learned to live with your post-nasal drip, it is best to be evaluated by a healthcare provider so you can get a proper diagnosis and the most effective treatment. Post-nasal drip can impact your quality of life as well as your performance at work or school.
