This year, prolonged extreme temperatures and seemingly never-ending snowstorms in the United States forced many inside, seeking shelter from what felt like an unusually long winter. This meant some of us were stuck in bed for a day or two clutching a box of Kleenex and downing cough syrup. That’s because viruses that cause the common cold love enclosed spaces with lots of people—the family room, the office, the gym.

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And though spring has arrived, cold-causing microbes haven’t slowed down. More than 200 viruses can trigger a runny nose, sore throat, sneezing and coughing—more than 1 billion cases of the common cold occur in the United States each year. The worst offenders (and the most common), known as human rhinoviruses, are most active in spring, summer and early fall.

While it’s difficult to pinpoint exactly when infected people cease to be contagious, they’re most likely to spread their cold when symptoms are at their worst, explains Dr. Teresa Hauguel of the National Institute of Allergy and Infectious Diseases. However, there’s another window of opportunity to be wary about. “A person can be infected before they actually develop symptoms, so they can be spreading it without even realizing it if they’re around people,” Hauguel writes in an email.

Surprised? Here are five more facts about the common cold.

Cold-causing viruses can be found in all corners of the world. Rhinoviruses (from the Greek word rhin, meaning “nose”) evolved from enteroviruses, which cause minor infections throughout the human body. They have been identified even in remote areas inside the Amazon. But it’s impossible to tell how long humans have been battling colds. Scientists can’t pinpoint when rhinoviruses evolved: they mutate too quickly and don’t leave a footprint behind in preserved human fossils. They could have been infecting mankind hominids before our species appeared. Or they might have sprung up as small groups of humans moved out of isolation and into agricultural communities, where the pathogen became highly adapted to infecting them.

Cold-causing microbes can survive for up to two days outside of the body. Rhinoviruses, which cause 30 to 50 percent of colds, usually live for three hours on your skin or any touchable surface, but can sometimes survive for up to 48 hours. The list of touchable surfaces is a lengthy one: door knobs, computer keyboards, kitchen counters, elevator buttons, light switches, shopping carts, toilet paper rolls—the things we come in contact with on a regular basis. The number of microbes that can grow on these surfaces varies, but each spot can contain several different types of microbes.

You can calculate how far away to stand from someone who’s sick. When a sick person coughs, sneezes or talks, they expel virus-containing droplets into the air. These respiratory droplets can travel up to six feet to another person. A recent study found that the largest visible distance over which a sneeze travels is 0.6 meters, which is almost two feet. It did so at 4.5 meters per second, about 15 feet per second. A breath travels the same distance but much slower, at 1.4 meters—4.5 feet—per second. Moral of the story: remain six feet from infected people, and move quickly when they gear up to sneeze.

The weather plays a role in when and how we get sick—but not in the way you might think. Humidity levels can help those droplets whiz through the air quicker: the lower the humidity, the more moisture evaporates from the droplet, shrinking it in size so it can stay airborne for larger distances. Cold weather is notoriously dry, which explains why we’re more likely to catch a cold while we huddle up inside when temperatures start sinking. This type of air can dry out the mucus lining in our nasal passages; without this protective barrier that traps microbes before they enter the body, we’re more vulnerable to infection. So we’re weakened by the air we breathe in when it’s chilly out, not the chilly weather itself.

Contrary to popular belief, stocking up on vitamin C won’t help. Linus Pauling, a Nobel Prize-winning chemist, popularized the idea of taking high doses of vitamin C to ward off colds. But when put to the test, this cold remedy doesn’t actually work. If you take at least 0.2 grams of vitamin C every day, you’re not likely to have any fewer colds, but you may have colds that are a day or two shorter. When symptoms start to appear, drizzling packets of Emergen-C into glass after glass of water won’t help either. The vitamin is no more effective than a placebo at reducing how long we suffer from cold symptoms.