Why is my chicken sneezing?

Often the coop rather than the bird. Chickens kick up enormous amounts of dust, and litter that has gone damp produces ammonia — if you can smell it at roost height it is already concentrated enough to damage the lining of the airway, and the fix is ventilation and dry bedding rather than medicine. It becomes an infection question when the sneeze arrives with company: foam or bubbles in the eye, rattling breath, discharge crusting the nostrils, or swelling around the face. One bird sneezing occasionally in a dusty run is very different from three birds rattling at night.

What is the difference between mycoplasma and infectious coryza?

The sourced difference is the course, not the smell. Merck gives infectious coryza an incubation of 1-3 days and a typical illness of 2-3 weeks, with decreased activity, nasal discharge, sneezing and facial swelling that can close an eye. Mycoplasma gallisepticum is chronic: rales, difficulty breathing, coughing, sneezing, discharge and conjunctivitis, with high morbidity and low mortality — and infected birds "remain infected for life". So coryza arrives fast and passes; mycoplasma stays. You will read that foul-smelling discharge identifies coryza. Merck describes a serous discharge and never mentions odour, so we do not use smell as a test.

Can chickens recover from a respiratory infection?

They can look completely recovered and still be infectious, which is the part that catches keepers out. For mycoplasma, Merck states that antibiotics such as tylosin and tetracyclines "may alleviate clinical signs and lesions but do not eliminate infection", and that infected birds remain carriers. Coryza is similar in this respect — Merck notes that chronically ill and healthy carrier birds are the reservoirs of infection. So a course of medication treats the signs, not the status. That is why the diagnosis matters more than the treatment.

What antibiotics treat chicken respiratory infections?

That is a veterinary decision, and deliberately not something we will hand you a dose for. For coryza, Merck names erythromycin and oxytetracycline as commonly used, along with sulfonamides including trimethoprim-sulfamethoxazole; for mycoplasma, tylosin and tetracyclines. But which drug, at what dose, for how long, and with what egg-withdrawal period depends on the diagnosis, your country's rules on veterinary antibiotics, and whether the birds are laying. Guessing at antibiotics also selects for resistance in a flock you may keep for years.

Should I cull a chicken with a respiratory infection?

It is a genuine decision rather than an obvious one, and it turns on the diagnosis rather than on how sick the bird looks. If a flock tests positive for mycoplasma, every bird is a lifelong carrier, so the realistic options are a permanently closed flock — no birds or hatching eggs leaving, ever — or depopulating and starting again from mycoplasma-free stock. Plenty of backyard keepers choose the closed flock and their birds live normal lives. What does not work is treating, assuming it is over, and then selling chicks.

How do I stop respiratory disease spreading through the flock?

Separate the affected bird the moment you notice, because both organisms travel on aerosols and respiratory secretions and a coop is a small shared airspace. Then open the high vents: damp, still, ammonia-heavy air makes every respiratory condition worse, and ventilation above the birds removes moisture without putting a draft across the roost. Quarantine any new bird for weeks before introducing it — buying in a carrier is the most common way this arrives in a healthy backyard flock.

Chicken Sneezing & Respiratory Infection

Most single sneezes are dust. The ones that matter come with company — and the reason to get a diagnosis is not the treatment, it is what the diagnosis commits you to.

Figures reviewed against published veterinary guidance · Last reviewed August 2026

First: is it the coop or the bird?

Before reaching for anything, go into the coop and put your face down at roost height. Chickens generate a startling amount of dust, and litter that has gone damp produces ammonia — if you can smell it at bird level, it is already concentrated enough to damage the lining of the airway and make a healthy bird sneeze.

That is a ventilation problem, not an infection, and the fix costs nothing: open vents above the birds so damp air leaves, and get the bedding dry. Roughly 12 square inches of high open vent per bird is the figure from University of Maine Extension's winter guidance. Our ventilation guide explains why the rule you will find quoted everywhere else has no source.

When a sneeze is actually a disease

The pattern to watch for is a sneeze that has company:

Foam or bubbles in the eye — the sign that most reliably moves this out of the dust category.
Rattling or wheezing breath. Easiest to hear in a quiet coop after dark, when the birds have settled.
Discharge crusting the nostrils shut.
Swelling around the face, sometimes closing an eye.
Open-mouth breathing at rest in normal temperatures. This one is an emergency, not a symptom to research.

Any of these means the bird comes out of the flock today. Both of the organisms below travel on aerosols and respiratory secretions, and a coop is one small shared airspace. Our symptom checker will tell you how urgent your particular combination is.

Mycoplasma vs coryza — the honest difference

Two organisms account for most backyard respiratory disease, and keepers spend a lot of effort trying to tell them apart from the outside. Here is what the sources actually support.

Infectious coryza — fast, then over

Caused by Avibacterium paragallinarum. Merck lists decreased activity, nasal discharge, sneezing and facial swelling, with the eye able to close from swelling of the infraorbital sinus. Incubation is 1–3 days and the illness typically runs 2–3 weeks. Merck names erythromycin and oxytetracycline as commonly used treatments, along with sulfonamides.

Mycoplasma gallisepticum — chronic, and permanent

Merck describes rales, difficulty breathing, coughing and/or sneezing, with nasal discharge and conjunctivitis; morbidity is high and mortality low in uncomplicated cases. Adult birds may show nothing at all without a secondary infection. It spreads both vertically, from hen to chick through the egg, and horizontally on aerosols.

And then the sentence that matters more than any treatment: infected birds "remain infected for life" and act as carriers. Antibiotics "may alleviate clinical signs and lesions but do not eliminate infection."

The test we will not give you

"Foul-smelling discharge means coryza" is repeated across almost every backyard poultry site. Merck's coryza entry describes a serous discharge and never mentions odour at all. So we do not use smell as a test. The sourced difference is the course: coryza incubates in days and passes in weeks; mycoplasma is for life. If you need to know which, that is a lab test, not a sniff.

Why the diagnosis matters more than the medicine

This is the part most guides skip, and it is the part that actually changes what you do. A mycoplasma-positive flock is a lifelong carrier flock. That means a treated bird who looks perfectly well is still infectious, and the realistic choices are:

A permanently closed flock. No birds and no hatching eggs ever leave. You can still keep chickens happily for years — plenty of people do — but you cannot sell, gift or swap them, and every new bird you add joins a carrier flock.
Depopulate and restart from mycoplasma-free stock, with the coop cleaned and rested.

What does not work is the middle path most people take by accident: treat, watch the signs disappear, assume it is over, and then sell a few chicks in spring. That is how this moves between backyard flocks.

It is also why we give no doses on this page. Which antibiotic, at what dose, for how long, and with what egg-withdrawal period is a veterinary decision that depends on the diagnosis and on your country's rules — and guessing at antibiotics breeds resistance in a flock you may keep for a decade.

Keeping it out in the first place

Quarantine every new bird for weeks, well away from the flock. Buying in a healthy-looking carrier is the single most common way this arrives.
Ventilate high, block drafts low. Damp still air is what makes a minor exposure into an outbreak.
Be careful at swaps and shows, and with borrowed equipment.
Ask where your chicks came from. Merck's stated control for mycoplasma is sourcing from free breeder flocks plus biosecurity — because infected birds cannot be cured.

A worked example

Nine hens. One has been sneezing for two days; this morning there is froth in the corner of her left eye. It is November, the coop was closed up against the cold three weeks ago, and the bedding by the waterer is damp.

Two things are true at once. The closed coop and damp litter are a real problem and would make any bird sneeze — so the high vents go open today regardless. But froth in the eye is not a dust sign, so she comes out of the flock as well, and this becomes a call to a vet rather than a bedding change.

The question worth asking before anything else: did anything new arrive recently? If three pullets came home from a swap five weeks ago, that is the likeliest route in, and it also tells you the other eight birds have already been exposed. Treating one bird in isolation would be the wrong mental model.

Sources

Clinical signs, incubation periods, carrier status and the named antibiotics are all quoted from the Merck Veterinary Manual entries for each organism. We deliberately do NOT repeat the widespread claim that foul-smelling discharge identifies coryza: Merck describes a serous discharge and never mentions odour. No doses are given here — that is a veterinary decision, and an invented dose is worse than an admitted gap.

Merck Veterinary Manual — Mycoplasma gallisepticum Infection in Poultry
Merck Veterinary Manual — Infectious Coryza
Merck Veterinary Manual — Common Infectious Diseases in Backyard Poultry
UC Davis Veterinary Medicine — Backyard Poultry Health and Disease Identification
Poultry Extension (Small and Backyard Flocks) — Ventilation in Small and Backyard Poultry Flock Housing
University of Maine Extension — Winter Care of Backyard Chickens (Bulletin #2026)

Frequently asked questions

Why is my chicken sneezing?: Often the coop rather than the bird. Chickens kick up enormous amounts of dust, and litter that has gone damp produces ammonia — if you can smell it at roost height it is already concentrated enough to damage the lining of the airway, and the fix is ventilation and dry bedding rather than medicine. It becomes an infection question when the sneeze arrives with company: foam or bubbles in the eye, rattling breath, discharge crusting the nostrils, or swelling around the face. One bird sneezing occasionally in a dusty run is very different from three birds rattling at night.
What is the difference between mycoplasma and infectious coryza?: The sourced difference is the course, not the smell. Merck gives infectious coryza an incubation of 1-3 days and a typical illness of 2-3 weeks, with decreased activity, nasal discharge, sneezing and facial swelling that can close an eye. Mycoplasma gallisepticum is chronic: rales, difficulty breathing, coughing, sneezing, discharge and conjunctivitis, with high morbidity and low mortality — and infected birds "remain infected for life". So coryza arrives fast and passes; mycoplasma stays. You will read that foul-smelling discharge identifies coryza. Merck describes a serous discharge and never mentions odour, so we do not use smell as a test.
Can chickens recover from a respiratory infection?: They can look completely recovered and still be infectious, which is the part that catches keepers out. For mycoplasma, Merck states that antibiotics such as tylosin and tetracyclines "may alleviate clinical signs and lesions but do not eliminate infection", and that infected birds remain carriers. Coryza is similar in this respect — Merck notes that chronically ill and healthy carrier birds are the reservoirs of infection. So a course of medication treats the signs, not the status. That is why the diagnosis matters more than the treatment.
What antibiotics treat chicken respiratory infections?: That is a veterinary decision, and deliberately not something we will hand you a dose for. For coryza, Merck names erythromycin and oxytetracycline as commonly used, along with sulfonamides including trimethoprim-sulfamethoxazole; for mycoplasma, tylosin and tetracyclines. But which drug, at what dose, for how long, and with what egg-withdrawal period depends on the diagnosis, your country's rules on veterinary antibiotics, and whether the birds are laying. Guessing at antibiotics also selects for resistance in a flock you may keep for years.
Should I cull a chicken with a respiratory infection?: It is a genuine decision rather than an obvious one, and it turns on the diagnosis rather than on how sick the bird looks. If a flock tests positive for mycoplasma, every bird is a lifelong carrier, so the realistic options are a permanently closed flock — no birds or hatching eggs leaving, ever — or depopulating and starting again from mycoplasma-free stock. Plenty of backyard keepers choose the closed flock and their birds live normal lives. What does not work is treating, assuming it is over, and then selling chicks.
How do I stop respiratory disease spreading through the flock?: Separate the affected bird the moment you notice, because both organisms travel on aerosols and respiratory secretions and a coop is a small shared airspace. Then open the high vents: damp, still, ammonia-heavy air makes every respiratory condition worse, and ventilation above the birds removes moisture without putting a draft across the roost. Quarantine any new bird for weeks before introducing it — buying in a carrier is the most common way this arrives in a healthy backyard flock.