We tend to view sinus pressure as a seasonal annoyance—a reason to buy decongestants and complain about the pollen count. We think of it as a "nose problem."

But anatomically, a sinus infection is a "head problem." Your sinuses are air-filled cavities nestled directly underneath your brain and between your eyes. In some places, the bone separating a pus-filled sinus from your brain's frontal lobe is as thin as an eggshell.

While rare, if a bacterial infection breaks through these thin walls, sinus pressure stops being a nuisance and becomes a medical emergency.

Here is how a standard sinus infection can turn dangerous and the signs that the barrier has been breached.

1. The Anatomy of Danger