Usually characterized as a dull ache or feeling of fullness, this pressure starts after an individual is up and about in the morning, then lasts until late in the afternoon. It is triggered when congestion of the nasal lining results in contact between adjacent structures in the nose and sinuses. When the opening to a sinus is blocked, the air within the sinus is absorbed and cannot be replaced because of the blockage. This results in a negative pressure within the sinus compared with the outside barometric pressure. This pressure, plus any accumulated secretions within the sinus, accounts for sinus headaches.
Diagnosis usually requires examination and an x-ray study of the sinuses.
Many common things cause changes in air pressure, with resultant sinus swelling and possible headache. Going up and down in an airplane subjects you to quick changes in atmospheric pressure. Even if you typically have no problems when flying, if you have an upper respiratory infection and decide to fly anyway, you may end up with a full-blown sinus infection because of the combination of nasal swelling from your cold and pressure changes in the airplane. Taking both an oral and a topical decongestant before takeoff may ameliorate this problem. Scuba diving, with its increased pressure underwater, can similarly lead to sinus swelling and infection.