Post-nasal drip happens when your nose and sinuses produce excess mucus, or when normal mucus doesn’t drain properly and instead pools and trickles down the back of your throat. Your nasal passages produce mucus constantly, roughly a quart per day, to trap particles and keep tissues moist. You swallow most of it without noticing. Post-nasal drip is what you feel when that process goes wrong, either because there’s too much mucus, it’s too thick, or something is blocking its normal path.
The causes range from seasonal allergies to acid reflux to the shape of your nasal anatomy. Understanding which one is driving your symptoms matters because the treatments are very different.
Allergies: The Most Common Cause
Allergic post-nasal drip is the single most frequent cause. When you inhale an allergen like pollen, dust mites, mold spores, or pet dander, your immune system overreacts. It releases chemicals that cause the mucus-producing cells lining your nasal passages to ramp up output. At the same time, blood vessels in your nasal tissue swell, which narrows the passages and makes it harder for mucus to drain forward through your nose. The excess has nowhere to go but backward, sliding down your throat.
Allergic post-nasal drip tends to follow seasonal patterns if pollen is the trigger, or persist year-round if it’s caused by indoor allergens like dust or pet dander. It often comes with sneezing, itchy eyes, and a watery quality to the mucus rather than thick or discolored drainage.
Sinus Infections: Viral vs. Bacterial
Both viral and bacterial sinus infections cause post-nasal drip, but they behave differently over time. A viral sinus infection, the kind that accompanies a common cold, typically starts improving after five to seven days. A bacterial sinus infection often persists for seven to ten days or longer, and can actually worsen after the first week.
One common misconception is that yellow or green mucus automatically signals a bacterial infection. That’s not reliable. Yellow and green mucus, fever, headache, and bad breath can all occur with viral infections too. The more telling difference is the timeline: if your symptoms plateau or get worse past the seven-day mark, bacteria are more likely involved. Infection-related post-nasal drip often feels thicker and heavier than the watery drainage you get with allergies. Chronic sinus inflammation, known as chronic rhinosinusitis, affects 5 to 12 percent of the general population and is a major driver of persistent drip that lasts months.
Acid Reflux That Reaches Your Throat
This one surprises people. A condition called laryngopharyngeal reflux (LPR) occurs when stomach acid and digestive enzymes like pepsin travel up past your esophagus and reach your throat. It only takes a small amount to cause problems, because the tissues in your throat lack the protective lining your esophagus has. They also don’t have the same mechanisms to wash reflux away, so the acid lingers and irritates the tissue longer.
LPR happens when the upper sphincter at the top of your esophagus relaxes when it shouldn’t, allowing reflux that’s already in your esophagus to creep higher. The irritation this causes in the throat often feels identical to post-nasal drip: a persistent sensation of something coating or stuck in the back of your throat, frequent throat clearing, and a mild cough. Many people with LPR-related drip never experience classic heartburn, which makes it easy to miss as a cause. If your post-nasal drip doesn’t respond to allergy or sinus treatments, reflux is worth investigating.
Non-Allergic Triggers: Food, Cold Air, and Irritants
Your nose can overproduce mucus in response to things that have nothing to do with allergies or infections. This falls under the umbrella of non-allergic rhinitis, and the triggers are surprisingly varied.
Spicy food is a classic example. Capsaicin and other compounds in hot food activate a nerve called the trigeminal nerve in your nasal lining. This triggers your nose to produce mucus and dilates blood vessels in the nasal tissue, causing swelling and congestion. Your body essentially reacts to the chemical heat the same way it would react to actual heat: widening blood vessels to release it. This is called gustatory rhinitis, and it’s harmless, though it can be annoying enough to seem like a real problem.
Cold, dry air works through a similar mechanism. When cold air hits the nasal lining, it stimulates mucus production as a protective response. Strong odors, cigarette smoke, perfume, cleaning chemicals, and changes in humidity or barometric pressure can all provoke the same reaction. If your drip consistently flares around specific environmental conditions rather than following an allergy pattern, non-allergic rhinitis is the likely explanation.
Structural Problems in the Nose
Sometimes the issue isn’t overproduction of mucus but a physical obstruction preventing normal drainage. A deviated septum, where the wall between your two nasal passages is significantly off-center, can impair sinus drainage. This creates a bottleneck that traps mucus, leading to recurrent sinus infections and chronic drip. Nasal polyps, which are painless growths on the lining of the sinuses, can block drainage pathways in the same way.
Structural causes are worth considering when post-nasal drip is constant, doesn’t respond to medications, and tends to affect one side more than the other. A deviated septum in particular often causes problems only on the narrower side.
Medications That Cause Nasal Congestion
Several types of medication can trigger or worsen post-nasal drip as a side effect. Blood pressure medications, anti-inflammatory pain relievers, and certain medications for erectile dysfunction are all associated with drug-induced rhinitis. The mechanism varies, but the result is the same: swollen nasal tissue, excess mucus, or both.
One especially common culprit is the overuse of over-the-counter nasal decongestant sprays. Using these for more than three to five consecutive days can cause rebound congestion, where the nasal tissue swells worse than before you started using the spray. This creates a cycle of increasing use and worsening symptoms that can be difficult to break.
Hormonal Changes
Your nasal tissue has receptors that detect hormones like estrogen. During pregnancy, rising hormone levels can cause these receptors to trigger blood vessel dilation and increased mucus production in the nose, leading to a condition called pregnancy rhinitis. It can feel like a perpetual stuffy nose with constant drip, and it often begins in the second or third trimester. It typically resolves after delivery.
Hormonal shifts during menstruation, puberty, or thyroid disorders can produce similar effects, though pregnancy rhinitis is the most well-documented version.
What the Drip Does to Your Throat
When post-nasal drip persists, the constant flow of mucus irritates the tissue at the back of your throat, including your tonsils and adenoids. Over time, this irritation causes the tissue to develop raised, bumpy patches that look like cobblestones or pebbles. This cobblestone appearance is a visible sign that drip has been ongoing and is actively inflaming the throat lining. The bumps may look discolored or swollen. They aren’t dangerous on their own, but they’re a useful clue when trying to confirm that post-nasal drip is actually happening versus other causes of throat discomfort.
Chronic drip can also cause a persistent cough, especially at night when lying flat allows mucus to pool, as well as hoarseness, a sore throat that comes and goes, and the feeling of constantly needing to clear your throat.