You expect your quads and calves to ache after a 5-miler—but your teeth?

If your ivories have started aching while you’re out for a run, there are a few potential reasons why, says Jeffrey Laubmeier, D.M.D., dentist in Lakewood, Ohio, and member of the Academy for Sports Dentistry.

Let’s start with the good: As your feet hit the ground when you run, the force of impact travels upward through your body. If you're clenching your jaw or gritting your teeth, you'll feel that pressure in your pearly whites, Laubmeier explains. That's the most common culprit behind teeth pain, he adds, and easily fixable: make sure your shoes aren’t worn through, to optimize shock absorption, and try to not clench as you pound the pavement.

But aching teeth mid-run could also be a sign of a few different health concerns, Laubmeier warns. For one, the pain could be early signs of a sinus infection. In many people, the roots of the upper teeth protrude into the maxillary sinuses, the largest sinus cavities located below the cheeks and on the sides of your nose. “If the sinus lining is irritated or infected, then the nerves entering the roots of the teeth can be as well,” he explains. “Then, when the feet make an impact with the ground, the nerves of the teeth can be stimulated and cause a sharp pain.”

Pain on a run can also be a sign of dental issues—namely, an infection or cavity. When you work out in any form, it increases your blood pressure, and the boost in blood flow can exacerbate an existing dental infection, Laubmeier explains.

A cavity, on the other hand, would be painful because of exposure to air as you inhale and exhale. Remember: Cavities are basically just holes in your teeth, and that means liquids, air, food, and bacteria make their way inside. When you run—especially when it’s cold outside—breathing pulls cold air into your mouth and through your tooth, stimulating the nerves and causing pain, he says.

Unfortunately, most of us won’t be able to tell the difference between tooth pain from a sinus infection and from a dental infection until whichever it is becomes fully blown. But you can at least use the ache as an early alarm for other symptoms developing. If the problem persists, ask your dentist, Laubmeier advises. He or she can take an X-ray to either diagnose or to rule out the red flags and confirm you just need to relax your jaw while logging miles.