Postnasal Drip: Allergy or Sinusitis? A Guide to Telling Them Apart

Postnasal drip is one of the complaints we see most often in ENT practice. But there is an important point:

Postnasal drip does not make a diagnosis by itself.

The symptom occurs in both allergic rhinitis and sinusitis. Most patients interpret postnasal drip directly as sinusitis, but clinically that is not always right. For a correct diagnosis, the character of the discharge, the accompanying findings and the clinical course have to be assessed together.

Why does postnasal drip occur?

Postnasal drip develops through two basic mechanisms.

In allergic rhinitis:

• Allergic inflammation of the nasal lining
• Increased secretion plus heightened nerve sensitivity

In sinusitis:

• Inflammation or infection in the sinuses
• Impaired drainage and a build-up of secretions

Clinically, the most important difference is the character of the discharge.

Postnasal drip in allergic rhinitis

• Thinner and watery
• Usually arising from the front of the nose
• Patients tend to describe “a constant need to clear my throat” or “a slight feeling of dripping”

Postnasal drip in sinusitis

• Thicker and stickier (sometimes purulent)
• Comes from the sinuses (especially the middle meatus)
• More pronounced: fullness in the throat, a bad taste or smell, a feeling of heavy discharge

A point worth stressing

Postnasal drip can be seen:

• in allergic rhinitis
• in sinusitis
• and, in some patients, in reflux

In a significant proportion of patients who come to the clinic with postnasal drip, imaging shows no sinusitis. Starting antibiotics on the basis of this symptom alone is therefore not the right approach. “I have postnasal drip, so I have sinusitis” is not correct.

Why does endoscopy matter?

One of the most valuable findings of academic studies is that where the discharge comes from points to the diagnosis:

• Nasal cavity / turbinates → usually allergy
• Middle meatus / sphenoethmoidal recess → sinusitis

For this reason, endoscopic examination is the gold standard in postnasal drip.

What do we look at during the examination?

One of the most distinguishing points in the clinic is seeing where the discharge comes from.

• Thin secretions seen at the front of the nose and on the turbinates are more consistent with allergy
• Thick secretions coming from the middle meatus or the sinus drainage pathways suggest sinusitis

Endoscopic examination, done when needed, is therefore very valuable in clarifying the diagnosis.

Can allergy set the stage for sinusitis?

Yes, and we see it often.

The swelling of the lining that develops in allergic rhinitis can impair sinus drainage, which over time can pave the way for sinusitis.

So in long-lasting “allergy-like” complaints, sinusitis may have been added to the picture.

When should you see a doctor?

I recommend an assessment if:

• Symptoms last longer than 10 days
• They improved at first and then got worse again
• Facial pain is marked
• There is fever
• The complaint is one-sided and severe

Conclusion

Postnasal drip is a common finding, but it does not make a diagnosis by itself.

• Itching, sneezing and watery discharge → more likely allergy
• Thick discharge, facial pain and feeling generally unwell → more likely sinusitis

The definite distinction is most often made at the examination.

References

Pratter, M. (2006). Chronic upper airway cough syndrome secondary to rhinosinus diseases (previously referred to as postnasal drip syndrome): ACCP evidence-based clinical practice guidelines. Chest, 129 1 Suppl, 63S-71S.

Bucher, S., Schmid‐Grendelmeier, P., & Soyka, M. (2019). Altered Viscosity of Nasal Secretions in Postnasal Drip. Chest.

Perez, H., Chan, N., Crawley, B., Krishna, P., Church, C., & Seiberling, K. (2023). The diagnostic workup of patients with a primary complaint of post-nasal drip. International Journal of Otorhinolaryngology and Head and Neck Surgery.

Smallwood, D., Ledford, D., Kennedy, D., & Lockey, R. (2024). Postnasal Drip. The journal of allergy and clinical immunology. In practice.