Q: After my last dive, I got a nosebleed. What could have caused this?

A: When I was a junior Navy officer my recreational dive buddy was the unit’s supply officer. He warned me that nearly every time he came up from a dive, there would be blood in his mask and advised me not to be concerned. He was right, but despite making dozens of dives with him, watching my dive buddy clear blood out of his mask as soon as we reached the surface was always a bit unnerving.

The source of my dive buddy’s blood was likely his sinuses. Polyps and inflammation are common in the sinuses. In fact, mucous plugs within the sinuses can cause sinus squeezes, resulting in very painful headaches during and after a dive. Many people suffer from chronic sinusitis, which leaves the lining of the sinuses inflamed and friable. The pressure changes from diving can injure this cell lining, and the result is bleeding from the sinuses. The other possible cause of a bloody nose can be the lining of the nose itself. Drying out the tissue lining the nasal passages can make it susceptible to bleeding from the slightest trauma. Something as subtle as pinching the nose during ear equalization can result in a nosebleed.

If the nosebleed is a one-time event, I would not be too concerned. If it becomes frequent, I would recommend having an ear, nose and throat surgeon look into your nose and sinuses with a special instrument in order to identify the source of the bleeding.

James L. Caruso is a 30-year veteran of the U.S. Navy, serving as ship’s doctor, undersea medical officer and flight surgeon. His experience includes a fellowship in Diving and Hyperbaric Medicine at Duke University Medical Center; today he is Denver's chief medical examiner.