Cat Respiratory Infection vs. Allergies: Key Differences

Both upper respiratory infections and allergies produce overlapping symptoms in cats — sneezing, watery eyes, some nasal discharge — which makes distinguishing between them based on symptoms alone genuinely tricky. A few contextual clues help narrow it down, though a definitive answer sometimes requires a vet visit either way.

Infections tend to have a more defined course: symptoms often appear somewhat suddenly, may include a low fever and reduced energy or appetite alongside the respiratory signs, discharge is more likely to progress from clear to thicker and colored over several days as the infection develops, and the whole episode typically resolves within one to two weeks. Infections are also more likely to follow a specific exposure — a new cat introduced to the household, a recent boarding stay, or a known outbreak in a shelter environment the cat came from.

Allergies tend to be more chronic or seasonal, without the fever or significant energy/appetite changes that often accompany an infection, and discharge tends to stay clear and watery rather than progressing to thick and colored. Allergy symptoms may recur at the same time each year (seasonal) or persist ongoing if the trigger is something present year-round, like dust or a specific litter.

What to do: If symptoms appeared suddenly with reduced energy or fever, and especially if there's a known recent exposure to other cats, an infection is more likely and generally resolves with supportive care and time, sometimes needing antibiotics if a bacterial component develops. If symptoms are chronic, seasonal, or lack fever and lethargy, allergies are more likely and worth discussing management options for. Either pattern lasting beyond two weeks, or any appetite loss, warrants a vet visit regardless of which cause seems more likely.

For more on the discharge itself as a diagnostic clue, here's what different colors and patterns can indicate.