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All About Decompression Sickness

Risk Factors, Prevention, and Treatment


Risk Factors

Every diver has a different level of risk of Decompression Sickness. Many risk factors are still not fully understood, but there are a few basic factors that doctors agree increase the chance of developing Decompression Sickness:

  • Bodyfat
    The theory is that nitrogen absorbs more easily into fat, so an overweight diver is at a greater risk of decompression sickness.
  • Exercise
    Interestingly, exercise has both a positive and negative effect. Exercise at least 12 hours before a dive seems to produce proteins that protect the body and decrease the risk of Decompression Sickness. On the other hand, exercise less than 12 hours before a dive can raise the number of gas micronuclei on which bubbles form and this increases the risk of Decompression Sickness. Exercise immediately after a dive increases the risk of bubbles forming as blood pressure is increased and bubbles can more easily be transferred from the venous to the arterial side of the circulatory system.
  • Gender
    Theoretically women should have a higher risk of Decompression Sickness due to the fact that women typically have a higher bodyfat content. However, this has not been proven in studies and it's possible that gender does not affect the chances of suffering from Decompression Sickness.
  • Age
    Generally, older people are at an increased risk of Decompression Sickness. This is due to less efficient circulatory and respiratory systems.
  • Fitness
    Fitness definitely decreases the risk of Decompression Sickness. A fitter body is able to tolerate more physical stress, including Decompression Sickness.
  • Dehydration
    Dehydration causes less blood to be available for gas exchange which makes it more difficult for the body to off-gas, increasing the risk of Decompression Sickness.
  • Injury and Illness
    Injury and illness can affect normal circulation, increasing the risk of Decompression Sickness.
  • Alcohol
    Consuming alcohol before or after a dive accelerates circulation which helps tissues to load with gas. Alcohol also dilates capillaries which can increase the rate of nitrogen released.
  • Carbon Dioxide
    Improper breathing can lead to elevated levels of carbon dioxide which interferes with the bodies ability to transport gas. This will lead to an increased chance of Decompression Sickness.
  • Cold
    It is generally believed by doctors that diving in cold water increases the risk of Decompression Sickness. This is due to the body working harder to keep warm as it becomes colder. Meaning that when the body is warmer it is able to absorb gas normally but as it becomes cold it has difficult offing the gas.
  • Altitude and Flying After Diving
    When ascending on land or in a plane, the atmospheric pressure changes and this increases the chances of Decompression Sickness. It is best not to ascend above 300 meters (1000 feet) or fly after diving. Consult the current flying after diving guidelines to know when it is safe to fly.
  • Patent Foramen Ovale (PFO) - Hole in the Heart
    As a fetus, a baby doesn't breathe and needs a way for blood to bypass the lungs until it is born. The body achieves this by having a small opening in the middle of the heart that allows blood to bypass the lungs. Normally, this hole would close within a year of birth, but in approximately 20-34 of people this does not happen, leaving a permanent opening in the heart. Usually, a flap grows over the opening and there is no effect. However, in some cases the flap allows blood to pass through the opening. This means that bubbles are more easily able to pass from the venous to the arterial side of the circulatory system, greatly increasing the risk of Decompression Sickness. It has been found that a large proportion of divers who suffered from Decompression Sickness had a PFO.
  • Reverse Profiles
    The jury is still out on reverse profiling, or making a deeper dive after a shallower dive. Theoretically it should increase the risk of Decompression Sickness, but this has not been proven scientifically. It would still be better to err on the side of caution.


    As there are many risk factors, there are also many methods of prevention. Here's a basic checklist that will help you lower your risk of suffering from Decompression Sickness:

    • Always ascend slowly and safely from every dive
    • Don't push your limits and do all required decompression stops
    • Keep physically fit and within a healthy weight range
    • Don't exercise within 12 hours of diving
    • Don't ascend to altitude or fly immediately after diving
    • Breathe normally throughout the dive, don't exert yourself or skip breathe
    • Make sure you're adequately hydrated before every dive
    • Don't drink alcohol before or after diving and never dive when hungover
    • Get checked out by a doctor to find out if you have a PFO
    • Avoid reverse profiling - just in case


    Immediate on the scene treatment consists of oxygen therapy and basic first aid. This should be followed as quickly as possible by recompression treatment in a recompression chamber. When treating Decompression Sickness the delay in beginning recompression treatment can be the biggest single cause of residual effects.


    PADI, Encyclopedia of Recreational Diving, 3rd Edition.
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