How long does a stuffy nose last for a 11 month old baby?

Varies: Could be as long as several weeks. Things to look for that would warrant more urgent need to be seen would be gasping for breath, or unable to suck on pacifier/bottle/breast. Of course if they start acting in a manner concerning to you, a visit to their doctor would be warranted.

Cause: Depending on the cause it could last from a few days to a permanent thing if it's a cold(uri) a few days will start subsiding if it's the dryness in the house a humidifier and saline nose spray will help clear if it's an allergy allergens must be removed usually at this age it's dust a stuffy nose is not serious if no cough and eating and sleeping are as usual if other symptoms a professional.

Depends: Small infants are troubled by small nasal passages that are easily narrowed/obstructed by infection or irritants. A cold will gradually improve over a week or so. If it has been aggravated by fumes from your cleaning agents, hair spray, plug ins, candles, dust etc. it could be continuous until you remove the offending "air pollution".Nasal wash out with saline drops can help.