Sneezing, congestion, and runny nose—these are all classic symptoms of both a cold and allergies, making it difficult to self-diagnose and treat either at home. But despite their similar symptoms, an allergic reaction is quite different from the common cold. By learning the subtle differences between the two, you can relieve your symptoms faster—shortening your days of sniffling. "Allergies are the immune system reacting to something that is normally harmless to most people—think: pollen, dog dander, and mold," says Lakiea Wright, M.D., M.A.T., M.P.H., board-certified internist, allergist, and immunologist at Brigham and Women's Hospital and medical director of U.S. Clinical Affairs at Thermo Fisher Scientific. When you encounter allergens, your body sees them as a threat, and "reacts by releasing a chemical called histamine," Wright explains. "Ultimately, this causes the allergic reaction and symptoms."
A cold, on the other hand, is always caused by a virus that enters the body through the eyes, mouth, or nose, or by touching contaminated people or objects, such as shaking the hand of someone with a cold. "This means a cold can be contagious, while allergies cannot, and symptoms of a cold could become severe, including a fever and body aches," says Wright. Here's how to tell the difference between the two after you're already sniffling and sneezy.
When Do Symptoms Appear?
While allergies and colds share similar symptoms, recording exactly when those symptoms first appear can help you narrow down what you're suffering from. "Keeping track of your symptom history, such as when and where symptoms occur, and for how long, is an important clue to help identify the main cause," Wright says. With allergies, symptoms may appear during peak pollen season—or after a visit to a friend's pet-filled house. On the flip side, symptoms that appear gradually over a day or two can point to a cold. "When symptoms occur suddenly or out of nowhere, an allergy is most likely to be the cause," explains Wright.
How Long Do Symptoms Last?
A cold can take a week or two to clear up. Allergies, on the other hand, can dissipate as soon as you remove yourself from the environment causing your symptoms—like a home with cat hair—or can persist for months if you're reacting to a change in the season, Wright says. "You should start to recover from a cold in a week or two," she reiterates. "If symptoms last longer than that, you could be continuously exposed to an allergen that you're reacting to."
Pay Attention to Symptom Differences
It's true: A cold and allergies do share many symptoms, such as a runny nose and sneezing, but there are a few distinctive symptoms that don't overlap between the two. For example, allergies can't cause a fever—only a cold can do that. And while colds can cause headaches and muscle aches, it's very rare for allergies to do so, says Wright. What's more, while you can experience a cough when suffering a cold or allergies, a cough caused by allergies is most often a dry cough without mucus. "[The cough] is a direct reaction to something your sensitive to in the airway," Wright explains. "Coughs from colds tend to be on the wetter side—that 'wetness' is actually mucus your body is trying to move out of your body." And itchy, watery eyes and an itchy nose are almost always caused by allergies, Wright adds.
If you suspect you suffer from allergies, you may want to consider getting an allergy test, Wright suggests. "Every spring millions of people seek out allergy relief through over-the-counter drugs without really knowing their diagnosis," she says. "But we've seen firsthand how life-changing it can be when you finally know what is causing those problems with breathing, itching, rashes, or congestion." Your primary care physician may be able to administer one—and if he or she can't, he or she should recommend an allergist to do so.