Decompression sickness is a condition that occurs when nitrogen that has been dissolved in the tissues and blood by high pressure forms bubbles as the pressure drops.

The primary components of air are oxygen and nitrogen. Since high-pressure air is compressed, each breath obtained at depth encompasses many more molecules than a surface breath. Since the body uses oxygen continuously, extra oxygen molecules inhaled under high pressure usually do not pile up. The extra nitrogen molecules, though, do pile up in the tissues and blood.

When the outside pressure decreases during the upswing from a dive or when passing through a compressed air environment, the accumulated nitrogen that can be released into the air forms bubbles in the blood and tissues. These bubbles can widen and induce tissue damage, or they can clog blood vessels in a wide range of organs, either straight or by provoking small blood clots. Pain and other symptoms are caused by a blood vessel blockage.


  • Type I decompression sickness
  • Type II decompression sickness


Decompression sickness symptoms usually appear later than those of air embolism and pulmonary barotrauma. Only half of the people with decompression experience signs within one hour of surfacing, but many experience signs within six hours. Signs usually appear gradually and take some time to take effect. The initial symptoms could be

  • Loss of appetite
  • Vague feeling
  • Fatigue
  • HeadacheĀ 

Type I decompression sickness

  • Rash
  • Itching
  • Extreme fatigue
  • Skin mottling
  • Swelling of the chest, arm, or abdomen

Type II decompression sickness

The more severe form of decompression sickness is characterized by neurologic symptoms ranging from minor numbness to paralysis and death.


The nature of the illnesses and their onset in relation to diving help doctors identify the sickness. Tests like CT scans or MRIs can determine brain or spinal cord abnormalities.


The majority of people fully recover from the sickness. Divers experiencing only skin mottling, itching, and fatigue usually do not require recompression, but they must be monitored because more severe issues may develop. It is suggested and may provide relief to breathe oxygen through a close-fitting face mask.

  • Recompression therapy
  • Oxygen

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