The common cold is a viral infection. More than 200 different viruses can cause it, and no bacterial pathogen is responsible for a typical cold. This distinction matters because it determines what treatments actually work and which ones are a waste of time.
Which Viruses Cause Colds
Rhinoviruses are the most common culprit, responsible for roughly 25 to 80 percent of colds depending on the season. Coronaviruses (not just SARS-CoV-2, but a whole family of milder strains) account for 10 to 20 percent of cases. Influenza viruses cause another 10 to 15 percent, and adenoviruses about 5 percent. The remaining cases are spread across a long list of less common respiratory viruses.
This is why you can catch multiple colds per year. Each infection may come from a completely different virus, and immunity to one doesn’t protect you from the others. It’s also why there’s no single vaccine for the common cold: the sheer number of viruses involved makes that impractical.
Why Antibiotics Don’t Help
Antibiotics kill bacteria. They do nothing against viruses. Taking an antibiotic for a cold won’t shorten your illness, reduce your symptoms, or prevent complications. The CDC states this plainly: antibiotics won’t help you feel better when you have a cold.
A large study at Norway’s Akershus University Hospital tracked over 2,100 patients hospitalized with viral respiratory infections and found that antibiotics did not reduce the risk of death within 30 days. In fact, patients who received antibiotics during their hospital stay were twice as likely to die in that window, likely because antibiotic use was a marker of sicker patients and because the drugs themselves carry risks without offering benefit against viruses. The researchers concluded that “fear of bacterial co-infections may be exaggerated” and that antibiotics can safely be withheld in most patients with viral respiratory infections.
Unnecessary antibiotic use also contributes to antibiotic resistance, making these drugs less effective when they’re truly needed.
The Green Mucus Myth
One of the most persistent beliefs, even among some healthcare providers, is that green or yellow mucus signals a bacterial infection. It doesn’t. Both viral and bacterial respiratory infections can produce discolored mucus. The color change comes from immune cells flooding the area and releasing enzymes as they fight the infection. It’s a sign your immune system is working, not a sign you need antibiotics.
According to Mayo Clinic, viruses cause the vast majority of colds in both children and adults, and antibiotics do nothing against them regardless of what color mucus you’re producing.
When Bacteria Do Get Involved
While the cold itself is always viral, it can occasionally set the stage for a secondary bacterial infection. A cold causes inflammation and fluid buildup in your sinuses, ears, and airways. That warm, moist environment can become a breeding ground for bacteria that are normally harmless in small numbers.
The most common bacterial complications are sinus infections, middle ear infections (especially in children), and less commonly, pneumonia. These are rare relative to the total number of colds people catch each year, but they do happen. A few signs suggest a bacterial infection may have developed on top of your cold:
- Symptoms that improve, then suddenly get worse. A cold that seemed to be fading but comes back with a new fever or worsening congestion may indicate bacteria have taken hold.
- Fever lasting more than four days. Viral colds can cause a mild fever early on, but it typically resolves within a couple of days.
- Symptoms persisting beyond 10 days without improvement. Most colds resolve in under a week. If you’re still feeling just as bad after 10 days, something else may be going on.
- Severe or localized pain. Intense pain concentrated around your sinuses, in one ear, or in your chest can point to a bacterial complication rather than the cold itself.
These are the situations where antibiotics become appropriate, because now there’s actually a bacterial target for them to work against.
How Viral and Bacterial Infections Feel Different
Viral colds tend to come on gradually. You might notice a scratchy throat one day, then a runny nose the next, followed by congestion and a mild cough. The whole illness builds over a few days, peaks, and slowly winds down over the course of a week or so.
Bacterial respiratory infections, by contrast, often hit harder and faster. Research from the Centre for Evidence-Based Medicine found that acute onset of symptoms is one of the strongest predictors of a bacterial rather than viral cause. Bacterial infections are also more likely to produce a higher fever, tender or swollen lymph nodes in the neck, and symptoms concentrated on one side of the body (one ear, one side of the sinuses, one lung).
That said, there’s enough overlap that you can’t reliably diagnose the cause based on symptoms alone. The pattern matters more than any single symptom.
What Actually Helps a Cold
Since a cold is viral, treatment is about managing symptoms while your body clears the infection. Over-the-counter pain relievers and fever reducers can take the edge off. Staying hydrated helps thin mucus and prevents dehydration, especially if you have a fever.
Honey is effective for relieving cough in adults and children over one year old. It should never be given to babies under one. For children under six, over-the-counter cough and cold medicines are not recommended and can cause serious side effects. Acetaminophen or ibuprofen for fever is fine for young children.
If your symptoms suggest you might have the flu or COVID-19 rather than a simple cold, getting tested early matters. Antiviral treatments exist for both, but they work best when started within the first couple of days of symptoms for the flu and within five to seven days for COVID-19. These antivirals target specific viruses and are not the same as antibiotics.
Most colds resolve on their own within a week. If yours doesn’t follow that pattern, or if symptoms come back worse after seeming to improve, that’s worth a conversation with your doctor to check for a bacterial complication that might actually benefit from antibiotics.