There are important differences between these common causes of nasal congestion, cough, and misery.
The common cold
Also called an “acute upper respiratory infection”, a “cold” usually starts with a vague ill feeling, followed by a sore throat and then a congested or drippy nose. Sometimes, there’s a fever at the start of the illness (that’s more common in babies and younger children.) A few days later, a cough begins. On average, the symptoms of a cold last about 10 days, though often the cough lingers for 2 or 3 weeks.
The symptoms of a cold grow or develop over several days, and the fever is really only at the beginning. By day 7-10 things start to improve.
Influenza
“The flu” is a specific viral infection, and it’s not just a bad cold. Symptoms including fever, sore throat, body aches, nasal congestion or drip, and cough all pretty much start all at the same time, or within a few hours. Sometimes there are also gastrointestinal symptoms like abdominal pain or vomiting. Fever and aches are usually the worst symptoms – you feel, pretty much, like you’ve been hit by a truck. The worst symptoms last five days, but the congestion and cough often linger for another week or so.
The symptoms of influenza are sudden and severe.
Sinusitis
Most common colds, of course, go away on their own, with or without any kind of treatment. But rarely a common cold can turn into a sinus infection. That occurs when the persistent mucus becomes infected with bacteria, leading to worsening symptoms 7-10 days into an ordinary cold, or persistent symptoms 2 weeks after a cold begins. Very rarely, sinusitis can start suddenly and severely, but much more typically there is first a cold that turns into a sinus infection.
A sinus infection is like a cold, but the symptoms worsen after 7-10 days.
Allergies
Allergies mostly causes nasal symtpoms, including stuffiness, congestion, dripping, and sneezing, along with an itchy sensation. Often there are eye symptoms as well. Allergies, alone, never cause a fever. Though there can sometimes be a cough or sore throat, those symptoms are less severe than the main, nasal symptoms.
Allergies cause mostly nasal symptoms, and no fevers.
This was adapted from a post on Dr. Roy’s blog—visit PediatricInsider.com for the full series of posts on this and many other topics.