It’s topical. If you’re not sick as a remnant of winter, or the weather changing suddenly, then you probably have allergies. I’m in the middle of a combination of those things, so here we go!
This information is taken from online medical sites as well as personal knowledge and experience. If it makes you sleep better at night, I am a licensed (and volunteering) EMT. I’m not trying to give you bogus information, but you should also check with your doctor before believing something you read on the internet.
The general rule is if it’s affecting you above your neck, you’re good to go; if it’s a chest thing, don’t do it. This means head colds, congestion, allergies, coughing are in the clear. Fevers, chest pain or congestion, lung infections, body ache, or anything below your throat should be treated differently. These symptoms require rest, and you should take it easy.
This view is supported by research done at Ball State University by Tom Weidner, Ph.D., director of athletic training research. In one study, Weidner took two groups of 30 runners each and inoculated them with the common cold. One group ran 30 to 40 minutes every day for a week. The other group was sedentary. According to Weidner, “the two groups didn’t differ in the length or severity of their colds.” In another study, he found that running with a cold didn’t compromise performance. He concluded that running with a head cold—as long as you don’t push beyond accustomed workouts—is beneficial in maintaining fitness and psychological well-being
However, you should also keep in mind that exercising intensely can escalate the severity of your symptoms. Besides, when you feel like crap, are you really likely to want to do all of the intervals? Take an easy run instead.
Want other opinions?:
Work Out with a Cold? (Mayo Clinic)
How to Run a Marathon While Getting Sick (LiveStrong)
Should I Run When I’m Sick? (The Complete Runner)