Nasal discharge is a triage question before it is a treatment question. Clear and watery in the first 48 to 72 hours is almost always viral. Yellow-green from day 5 to 7 means bacteria moved in behind the virus. Blood, or discharge from 1 nostril only, pulls foreign body, polyp, tumor, and clotting problems onto the list. Three facts settle most cases: color, how many days in, and whether 1 or 2 nostrils are running.
The 4 colors and the day each one shows up
| Color and texture | Usual cause | Typical day of illness | Act within |
|---|---|---|---|
| Clear, watery, 1 to 3 mL a day, both nostrils | Viral upper respiratory infection (FHV-1, FCV) | Day 1 to 3 | 72 hours |
| White, stringy mucus | Viral inflammation, mild | Day 3 to 5 | 48 hours |
| Yellow-green, thick, 2 to 5 mL, crusts on the nostril | Secondary bacteria, sinusitis | Day 5 to 10 | 24 hours |
| Brown-black, 1 to 2 mm crusts | Dried blood, mild trauma, foreign body | Any day | 24 hours |
| Bright red, fresh, 1 nostril only | Foreign body, mass, high blood pressure, rat poison | Any day | Same day |
| Pink-tinged froth with 5 or more sneezes in a row | Erosion of the nasal lining | Day 4 to 8 | 12 hours |
Volume carries its own signal: 1 to 3 mL of clear fluid a day is often tears draining through the tear duct, while 5 to 8 mL of thick yellow fluid is filling a sinus, and that much pus under pressure erodes bone in 2 to 4 weeks.
Clear discharge: the first 72 hours
Most clear discharge is herpesvirus or calicivirus, and the cat is contagious to other cats for 7 to 14 days. Herpesvirus also leaves 1 or 2 red, squinting eyes, because the same virus infects the conjunctiva. Keep the room at 40 to 60 percent humidity, wipe the nostrils 2 to 3 times a day with saline on gauze. That is enough for a cat that is still eating 30 to 40 g of food a day and drinking normally.
Two things turn clear discharge into a same-week visit: the cat stops eating for 24 hours, because a blocked nose kills appetite in 1 to 2 days, and the discharge is still clear on day 10. A viral infection that has not turned by day 10 to 14 is either not viral or has a second problem behind it.
Yellow-green: the day 5 to 7 switch
Color alone is a weak test. Thick yellow-green mucus on day 6, with a cat that still eats and has a temperature of 38.5 C, often needs no antibiotic at all. The combination that does need one is 3 findings together: thick discharge for 5 or more days, a temperature above 39.2 C, and 24 hours of reduced food intake. Most vets then prescribe 7 to 10 days of an antibiotic chosen for upper respiratory bacteria, and stop if the cat is normal at day 5.
Do not put human decongestant drops in a cat nose. Xylometazoline at 0.05 percent, 1 to 2 drops, can cause 12 hours of heavy sedation, high blood pressure, and a heart rate over 240. The same rule applies to eucalyptus and peppermint oils: 1 drop near the nose is enough to cause drooling and wobbling for 6 to 8 hours. If any of that happened, check the toxin list before you wait it out.
Blood: 3 causes worth separating
Fresh blood from 1 nostril, 1 to 3 mL, with 10 or more sneezes in a row, is a foreign body until proven otherwise: a 2 to 3 cm blade of grass, a foxtail, or a piece of chew toy wedged 2 to 4 cm up the passage. A polyp behaves the same but adds 3 to 6 weeks of one-sided snoring.
The second cause is a mass. Nasal tumors in cats cluster at 9 to 12 years, and the early sign is 1-sided blood-streaked discharge 2 to 3 times a week with no fever, not a single large bleed. The third is a clotting or pressure problem: rat poison shows up 3 to 7 days after the bait, and a systolic blood pressure over 180 mmHg can leak blood from the nose in an older cat with kidney or thyroid disease.
One nostril or two changes the list
Both nostrils running, plus sneezing and a low appetite, is a systemic or viral problem, and the answer usually sits in the mouth and eyes as well. One nostril, especially in an adult cat with normal appetite and no fever, is a structural problem: something is sitting in that passage. A 3-week history of one-sided discharge with 0 fever is the point where a scope beats a third round of antibiotics.
Check the eyes at the same time. Discharge that runs down the inside corner, a squinting eye, or a cloudy cornea belongs in the eye discharge guide, and a kitten with discharge, sneezing, and 39.5 C has the classic upper respiratory infection picture rather than an allergy.
Saline rinses: 1 to 2 mL, 2 to 3 times a day
Use 0.9 percent saline at room temperature, 1 to 2 mL per nostril, 2 to 3 times a day, which comes to 4 to 12 mL a day in total. Draw it into a 3 mL syringe with no needle, tip the head back 20 to 30 degrees, and aim at the outer wall rather than straight up the middle. Do it 5 to 10 minutes before a meal so the cat eats with a clear nose, and expect 2 to 3 sneezes afterward.
Three rules are not optional. Never use tap water, which carries chlorine and, rarely, organisms that survive in the nose. Never use a homemade mix stronger than 0.9 percent, because 3 percent salt stings and 0.3 percent does nothing at all. Never push more than 2 mL into one nostril at once in a cat under 3 kg, because the fluid can reach the throat and trigger a cough.
Nebulization: 10 to 15 minutes, 1 to 2 times a day
A nebulizer with 3 to 5 mL of saline for 10 to 15 minutes, 1 to 2 times a day, loosens crusts that a rinse cannot reach. Run it for 5 to 7 days. Without a nebulizer, use the bathroom: 10 to 15 minutes with the door closed, 10 minutes after the hot water is off, twice a day. Add nothing to the water. Essential oils, decongestants, and human saline nasal sprays with preservatives all irritate a 2 mm nasal passage that is already inflamed.
Go now: the 4 signs that outrank color
- Breathing 40 or more times a minute at rest, or any open-mouth breathing.
- No food for 24 hours, or 2 days of eating under half the usual ration.
- A temperature of 39.7 C or higher, or 37.5 C or lower.
- More than 5 mL of blood at once, or bleeding that runs past 10 minutes.
For everything else, 5 steps cover the first week: log color and volume once a day, rinse with 1 to 2 mL of saline 2 to 3 times daily, nebulize for 10 to 15 minutes twice daily, keep the room at 40 to 60 percent humidity, and book a visit if day 7 arrives with thick yellow discharge, 1-sided flow, or a cat that has lost interest in food.
Frequently asked
How do I know if yellow nasal discharge needs antibiotics?
Color by itself does not decide it. Most vets treat when 3 things line up: thick yellow-green discharge for 5 or more days, a temperature above 39.2 C, and 24 hours of reduced eating. With clear mucus on day 6 and a cat eating normally at 38.5 C, a saline rinse 2 to 3 times a day for 72 hours is often the whole plan.
Is one-sided nasal discharge in a cat serious?
It deserves a closer look because viruses hit both nostrils. One-sided flow in an adult cat with a normal appetite and no fever points to a foreign body, a polyp, or a mass, and 3 weeks of it is the point to scope rather than try another 6 weeks of tablets. Blood from one nostril is a same-day visit.
How often can I rinse a cat nose with saline?
One to 2 mL per nostril, 2 to 3 times a day, which is 4 to 12 mL a day, using 0.9 percent saline at room temperature. Do it 5 to 10 minutes before a meal, stop at 2 mL per nostril in cats under 3 kg, and never use tap water or a homemade mix stronger than 0.9 percent, since 3 percent salt stings and irritates.