How to tell a cold from the flu, explained

We are in the midst of what is shaping up to be the worst flu season in recent history. But many people coming down with sore throats and sniffles right now may be unsure if they have flu or one of the other nasty bugs, like the common cold, that make winter the sick season.

It’s actually pretty easy to tell the difference, according to this very handy “flu algorithm” going around on Twitter:

The message is: If you have the flu, you’ll know it by how utterly zapped of energy you feel. And the flu comes on abruptly, like a fast train running over you.

Really bad colds are often confused with flu, since they are also respiratory diseases. But the two have a different set of causes and symptoms.

There are four species of influenza viruses — A, B, C, and D — and seasonal flu is caused by influenza A and B. Every year, different strains of these A and B viruses circulate, but they all cause similarly severe symptoms: fever, chills, headache, fatigue, muscle pain, and sore throat.

Most people can just wait the flu out at home, getting lots of rest and taking care not to infect others. But certain people in high-risk groups — young children, pregnant women, elderly people over age 65, people with other chronic diseases — may want to seek medical attention.

The common cold, on the other hand, can be caused by many different viruses, most commonly rhinoviruses (and never flu viruses). Symptoms tend to be milder than flu; they come on gradually, rarely cause fever and chills, and are more likely to be marked by sneezes and a stuffy nose.

Colds also don’t generally lead to the serious health complications that can come with flu, and that in some cases can be deadly. In recent years, mild flu seasons tend to kill about 12,000 Americans, and severe flu seasons kill about 56,000.

For a more detailed breakdown on the difference between cold and flu, the CDC has a very useful infographic:

And what about “stomach flu,” you may wonder? Stomach flu isn’t flu at all; it’s an intestinal infection, which can be caused by viruses like norovirus or bacteria from food, and it leads to diarrhea, nausea, vomiting, and fever. If you want to get technical, “stomach flu” is actually a misnomer because there are no flu viruses involved. Instead, you should say gastroenteritis, or “stomach bug,” for this one.