The sinuses are pockets of mucous membranes around the face, most notably close to your nose. The exact number of them can vary from one person to the next, without any disadvantages to having fewer. Most of the time, you won't even be aware that your sinuses exist, but sometimes they can become inflamed, a condition known as sinusitis that can occur when you have a cold or the flu. Ordinarily, this isn't something to worry about, as it just causes a bit of discomfort for a week or so before going away on its own.