If your sinuses become congested during a dive, a reverse block can occur during ascent. This is a painful situation that causes air to expand against the inside of the sinus.

Most sinus reverse blocks occur when decongestant drugs wear off during a dive. For this reason, you should avoid using decongestant medications prior to a dive.

If a reverse block does occur, you should ascend as slowly as possible to allow time for the air to escape the congested sinus. If your air supply is low and you have to ascend, you might be able to equalize the sinus by closing your mouth, pinching your nose, and gently inhaling.