Why does pollen make you sneeze?
Pollen makes allergic people sneeze because mast cells in the lining of the nose carry IgE antibodies that recognize it: within minutes, they release histamine, which irritates nerves and makes the nose run. In 2021, 25.7% of US adults had a diagnosed seasonal allergy (CDC, 2023).
Simplified diagram for an adult with a pollen allergy. Relative levels: each curve has its own scale. All curves are estimates (dotted lines), drawn from the studies cited.
Why does pollen make you sneeze?
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Sources: bridge between two IgE antibodies, histamine within minutes, modest effect of antihistamines on a stuffy nose (Wheatley and Togias, N Engl J Med, 2015). Nerve, sneezing, and glands (Sarin, J Allergy Clin Immunol, 2006). Second wave 3 to 11 h later in 9 people out of 12 (Naclerio, N Engl J Med, 1985). Eosinophils in the late phase (Bascom, 1988). Antihistamines: inverse agonists of the H1 receptor (Church, 2013). Time shortened in step 1; sizes not to scale (IgE and histamine greatly enlarged).
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Frequently asked questions about pollen allergy
Pollen allergy or a cold: how can you tell the difference?
A pollen allergy differs from a cold mainly in how long it lasts and in the itching: a cold usually clears up in 1 to 2 weeks, while hay fever can last for weeks or months, as long as pollen is in the air (NHS). Itchy, watery eyes and sneezing fits point to an allergy, as do symptoms that come back in the same season every year. If in doubt, a doctor can suggest allergy tests.
How many people are allergic to pollen?
In the US, 25.7% of adults had a seasonal allergy diagnosed by a doctor in 2021 (CDC, 2023). In France, pollen allergy may affect up to 30% of adults and 7 to 20% of children, according to surveys compiled by Anses, the French health safety agency (2014). In Spain, the national allergy society counts more than 8 million people allergic to pollen (SEAIC, 2021). These figures come mostly from questionnaires without allergy tests: Anses warns that they probably overestimate the real numbers.
Why does your nose get stuffy several hours after pollen?
Your nose can get stuffy several hours after pollen because of a second wave of the allergic reaction, called the late phase. In a study where 12 allergic people had pollen placed in their noses, 9 had their symptoms return 3 to 11 hours later, with a new rise in histamine (Naclerio, 1985). White blood cells called eosinophils then arrive in the nasal lining (Bascom, 1988). It swells, and a stuffy nose takes over.
Does local honey help with pollen allergy?
Local honey has not been shown to help with pollen allergy: in a trial of 36 allergic people, neither local honey nor store-bought honey relieved symptoms more than a honey-flavored syrup (Rajan, 2002). The trial was small, but nothing today shows that honey desensitizes. The desensitization that has proven itself, immunotherapy, uses measured doses of pollen, prescribed by a doctor and started a few months before the season (NHS).
Pollen allergy: when should you see a doctor?
It is best to see a doctor if pollen allergy symptoms are severe, get worse, or if treatments don't relieve them or stop working (MedlinePlus, NHS). Wheezing, a tight chest, a cough that keeps coming back, or shortness of breath during exercise can be signs of pollen-related asthma, worth mentioning to a doctor (Santé.fr). Another tip: a decongestant nasal spray should not be used for more than 3 days in a row (MedlinePlus).
True or false?
Antihistamines stop your body from releasing histamine.
False. Histamine is still released; the drug sits on its H1 receptors to keep it from acting (Church and Church, 2013).
A steroid nasal spray works better than allergy pills.
True. Across 16 trials and 2,267 people, the steroid spray relieved a stuffy nose, runny nose and sneezing better than antihistamine pills (Weiner, 1998).
All antihistamines make you drowsy.
False. First-generation ones do. Second-generation ones barely enter the brain and cause much less drowsiness (Church and Church, 2013).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
What happens in the nose after pollen?
Within minutes, histamine causes sneezing and a runny nose. In some people with allergies, a second wave comes 3 to 11 hours later: this time, a stuffy nose takes over.
| Hours after pollen reaches the nose | Histamine in the nose (dotted) | Sneezing and itching (dotted) | Runny nose (dotted) | Stuffy nose (dotted) | Eosinophils in the nose (dotted) | What happens |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | Pollen arrives in the nose |
| 1 h | 18 | 12 | 38 | 41 | 8 | +1 h after pollen reaches the nose: early phase |
| 3 h | 10 | 6 | 15 | 32 | 25 | +3 h after pollen reaches the nose: late phase |
| 6 h | 29 | 12 | 32 | 77 | 66 | +6 h after pollen reaches the nose: late phase |
| 9 h | 16 | 8 | 20 | 70 | 88 | +9 h after pollen reaches the nose: late phase |
| 12 h | 5 | 4 | 9 | 42 | 95 | +12 h after pollen reaches the nose |
Key points
- Within minutes (Until +1 h, Shown in humans)
When pollen links two IgE antibodies on mast cells, the cells release histamine and other substances: symptoms start within minutes. Source: Wheatley and Togias, « Allergic rhinitis », N Engl J Med, 2015 - More histamine, more sneezing (Until +1 h, Shown in humans)
After pollen was placed in the noses of allergic people, the amount of histamine collected tracked the number of sneezes (105 tests in 35 people). Source: Naclerio et al., « Mediator release after nasal airway challenge with allergen », Am Rev Respir Dis, 1983 - Why we sneeze (Until +1 h 30 min, Shown in humans)
Histamine irritates the nerves in the nasal lining: itching, the sneeze reflex, and, through another reflex, glands pouring out mucus. Source: Sarin et al., « The role of the nervous system in rhinitis », J Allergy Clin Immunol, 2006 - A second wave, 3 to 11 h later (From +3 h to +11 h, Shown in humans)
In one study, 9 out of 12 allergic people had their symptoms return 3 to 11 hours after the pollen, with a new rise in histamine. Source: Naclerio et al., « Inflammatory mediators in late antigen-induced rhinitis », N Engl J Med, 1985 - Where does the histamine in the second wave come from? (From +3 h to +11 h, Hypothesis)
The authors see it mainly as the work of basophils, white blood cells related to mast cells: a substance made only by mast cells, prostaglandin D2, did not rise again. Source: Naclerio et al., « Inflammatory mediators in late antigen-induced rhinitis », N Engl J Med, 1985 - Eosinophils arrive (From +4 h, Shown in humans)
During this late phase (4 to 11 h), white blood cells flood into the nose: eosinophils, but also neutrophils and others. Eosinophils even start rising within the first 3 hours. Source: Bascom et al., « The influx of inflammatory cells into nasal washings during the late response to antigen challenge », Am Rev Respir Dis, 1988
What does an antihistamine change?
An antihistamine doesn't hold histamine back: it occupies its H1 receptors. Sneezing and a runny nose ease, a stuffy nose much less.
| Hours after pollen reaches the nose | Histamine in the nose (unchanged) (dotted) | Sneezing, no treatment (dotted) | Sneezing, with an antihistamine (dotted) | Stuffy nose, no treatment (dotted) | Stuffy nose, with an antihistamine (dotted) | What happens |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | Pollen arrives in the nose |
| 1 h | 18 | 12 | 4 | 41 | 35 | +1 h after pollen reaches the nose: early phase |
| 3 h | 10 | 6 | 2 | 32 | 27 | +3 h after pollen reaches the nose: late phase |
| 6 h | 29 | 12 | 4 | 77 | 66 | +6 h after pollen reaches the nose: late phase |
| 9 h | 16 | 8 | 2 | 70 | 60 | +9 h after pollen reaches the nose: late phase |
| 12 h | 5 | 4 | 1 | 42 | 36 | +12 h after pollen reaches the nose |
Key points
- Histamine is still released (Throughout, Shown in humans)
H1 antihistamines don't stop it from leaving the mast cell. They sit on the H1 receptor and keep it at rest: they are called inverse agonists. Source: Church and Church, « Pharmacology of antihistamines », Indian J Dermatol, 2013 - Less sneezing (Until +2 h, Shown in humans)
They work fast enough to be taken as needed, mostly for sneezing, itching, and a runny nose. Source: Wheatley and Togias, « Allergic rhinitis », N Engl J Med, 2015 - A stuffy nose changes little (From +3 h, Shown in humans)
Their effect on symptoms, especially a stuffy nose, is modest. Source: Wheatley and Togias, « Allergic rhinitis », N Engl J Med, 2015 - Older ones cause drowsiness (Throughout, Shown in humans)
First-generation antihistamines reach the brain: drowsiness, poorer attention. Second-generation ones barely get in. Source: Church and Church, « Pharmacology of antihistamines », Indian J Dermatol, 2013 - "With" curves: estimates (Throughout, Hypothesis)
How much symptoms drop varies by person and product; these curves are only an illustration.
What does a steroid nasal spray change?
A steroid (corticosteroid) spray calms inflammation in the nasal lining. Used every day during the season, it mainly reduces the second wave and a stuffy nose.
| Hours after pollen reaches the nose | Stuffy nose, no treatment (dotted) | Stuffy nose, with the spray (dotted) | Eosinophils, no treatment (dotted) | Eosinophils, with the spray (dotted) | Sneezing, with the spray (dotted) | What happens |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | Pollen arrives in the nose |
| 1 h | 41 | 25 | 8 | 2 | 4 | +1 h after pollen reaches the nose: early phase |
| 3 h | 32 | 16 | 25 | 8 | 2 | +3 h after pollen reaches the nose: late phase |
| 6 h | 77 | 28 | 66 | 20 | 4 | +6 h after pollen reaches the nose: late phase |
| 9 h | 70 | 26 | 88 | 27 | 2 | +9 h after pollen reaches the nose: late phase |
| 12 h | 42 | 18 | 95 | 29 | 1 | +12 h after pollen reaches the nose |
Key points
- The most effective treatment (Throughout, Shown in humans)
In 16 trials (2,267 people), steroid nasal sprays relieved a stuffy nose, runny nose, sneezing, and nasal itching better than antihistamine pills. Source: Weiner et al., « Intranasal corticosteroids versus oral H1 receptor antagonists in allergic rhinitis », BMJ, 1998 - Not within minutes (Throughout, Shown in humans)
The effect shows up in about a day; for year-round allergies, it takes several weeks of regular use to reach its full effect. Source: Wheatley and Togias, « Allergic rhinitis », N Engl J Med, 2015 - Fewer eosinophils (From +4 h, Shown in humans)
In allergic people given a steroid pill (prednisone) for the 2 days before, the influx of eosinophils in the late phase was blocked, but not that of other white blood cells. A steroid nasal spray also contains a corticosteroid, like prednisone, but it works mostly where it is sprayed, at a low dose; this study did not test it. Source: Bascom et al., « The influx of inflammatory cells into nasal washings during the late response to antigen challenge », Am Rev Respir Dis, 1988 - "With" curves: estimates (Throughout, Hypothesis)
An illustration of a treatment taken every day for several days, not a measurement.
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