Cold and flu have become an inseparable pair, like salt and pepper or New Year's and weight loss. Walking down the "cold and flu" aisle of any drugstore, you will find stacks of bright boxes with bold claims of help for those suffering from a cold or the flu. Since the two illnesses share some similar symptoms, and both come during "cold and flu season," the two often run together in people's minds. We have a vague idea that they are different, but if pressed, have a hard time saying exactly how. The significant distinctions between these two common conditions elude most of us, but the question is rarely raised.

The symptoms we get during a viral illness are often the body's attempt to get rid of the virus and to minimize damage. Sneezing ejects the virus from the nose, cough from the lungs and throat, vomiting from the stomach, and diarrhea from the intestines. Fever makes it difficult for the virus to reproduce. The topic of viral illnesses will always remain somewhat confusing, since the body has a relatively small number of symptoms with which to respond to an ever-changing, wide variety of viruses. While colds and flus may overlap, the differences between them are important.

The common cold is centered in the nose.

Over 200 different types of viruses can cause a cold. Rhinoviruses, which means "nose viruses", are the most common cause. Respiratory syncitial viruses (RSV) and a host of others can produce colds. Of note, influenza viruses occasionally cause illnesses with symptoms of the common cold.

The three most frequent symptoms of a cold are nasal stuffiness, sneezing, and runny nose. Throat irritation is often involved (but not with a red throat). Adults and older children with colds generally have minimal or no fever. Infants and toddlers often run a fever in the 100 to 102 degree range.

Depending on which virus is the culprit, the virus might also produce a headache, cough, postnasal drip, burning eyes, muscle aches, or a decreased appetite, but in a cold, the most prominent symptoms are in the nose. (By the way, forcing a child to eat with a decreased appetite due to a cold is both unnecessary and unhelpful, but do encourage drinking plenty).

If anything, using the term "common" with cold is an understatement. Colds are the most prevalent infectious disease. Children average 3 to 8 colds per year (younger children and boys are on the higher end of the range). Colds occur mostly in the winter (even in areas with mild winters). In areas where there is no winter, colds are most common in the rainy season. Parents get about half as many colds as their children do. Moms tend to get at least one more cold per year than Dads.

When someone has a cold, the nasal secretions are teeming with cold viruses. Coughing, drooling, and talking are all unlikely ways to pass a cold. But sneezing, nose-blowing, and nose-wiping are the means by which the virus spreads. You can catch a cold by inhaling the virus if you are sitting close to a sneeze, or by touching your nose, eyes, or mouth after you have touched something contaminated by infected nasal secretions.

Once you have "caught" a cold, the symptoms begin in 1 to 5 days. Usually irritation in the nose or a scratchy feeling in the throat is the first sign, followed within hours by sneezing and a watery nasal discharge.

Within one to three days, the nasal secretions usually become thicker and perhaps yellow or green -- this is a normal part of the common cold and not a reason for antibiotics. During this period, children's eardrums are usually congested, and there may well be fluid behind the ears -- whether or not the child will end up with a true bacterial infection. Yes, antibiotics are too frequently prescribed for this as well.

The entire cold is usually over all by itself in about 7 days, with perhaps a few lingering symptoms (cough) for another week. If it lasts longer, consider another problem, such as a sinus infection or allergies.

While it lasts, the common cold is primarily a head cold. While you may feel tired or have aches, the illness is centered in the nose, and most of the symptoms are above the neck.

With the flu, you are sick all over.

The flu can be a much more serious illness. The most deadly recent worldwide outbreak was the flu epidemic at the beginning of this century and killed more than 20 million people. Even today, more than 36,000 people in the United States die from the flu each year -- primarily those who are weak from advanced age or a major illness.

A single family of viruses -- the influenza viruses -- causes the flu. Most people get the flu once every year or two or three, and the illness is unpleasant but not usually dangerous. Unlike the common cold, both adults and children with the flu generally have a fever.

The flu can take many forms, but here we will describe the most typical:

Classically, the flu begins abruptly, with a fever in the 102 to 106 degree range (with adults on the lower end of the spectrum), a flushed face, body aches, and marked lack of energy. Some people have other systemic symptoms such as dizziness or vomiting. The fever usually lasts for a day or two, but can last five days.

Somewhere between day 2 and day 4 of the illness, the "whole body" symptoms begin to subside, and respiratory symptoms begin to increase. The virus can settle anywhere in the respiratory tract, producing symptoms of a cold, croup, sore throat, bronchiolitis, ear infection, and/or pneumonia.

The most prominent of the respiratory symptoms is usually a dry, hacking cough. Most people also develop a sore (red) throat and a headache. Nasal discharge and sneezing are not uncommon. These symptoms (except the cough) usually disappear within 4 to 7 days. Sometimes there is a second wave of fever at this time. The cough and tiredness usually lasts for weeks after the rest of the illness is over.

Inhaling droplets from coughs or sneezes is the most common way to catch the flu. Symptoms appear 1 to 7 days later (usually 2-3 days). The flu is airborne and quite contagious, and with its short incubation period it often slams into a community all at once, creating a noticeable cluster of school and work absences. The flu usually arrives in the winter months. Within 2 or 3 weeks of its arrival, most of the classroom has had it.

The other major difference between the common cold and the flu is that the flu is preventable. In any given year, two or three different strains of influenza virus cause most of the flu around the world. Each year, scientists gather extensive global data and formulate a vaccine for the strains anticipated to be the major problems in the coming winter. While the prediction is usually accurate, sometimes new, unanticipated strains arise. In other words, in some years the vaccine works better than in others.

If you do opt for a flu vaccine, It's preferable to use versions of the vaccine without added thimerosal (a form of mercury) as a preservative. Most kids still get the flu vaccines with extra mercury. You might have to request ‘no added mercury’ to get the vaccine you want.