The following environmental factors have been shown to increase the risk of DCS:

- the magnitude of the pressure reduction ratio – a large pressure reduction ratio is more likely to cause DCS than a small one.

- repetitive exposures – repetitive dives within a short period of time (a few hours) increase the risk of developing DCS. Repetitive ascents to altitudes above within similar short periods increase the risk of developing altitude DCS.

- the rate of ascent – the faster the ascent the greater the risk of developing DCS. The US Navy Dive Manual indicates that ascent rates greater than about when diving increase the chance of DCS, while recreational dive tables such as the Bühlmann tables require an ascent rate of with the last taking at least one minute. An individual exposed to a rapid decompression (high rate of ascent) above has a greater risk of altitude DCS than being exposed to the same altitude but at a lower rate of ascent.

- the duration of exposure – the longer the duration of the dive, the greater is the risk of DCS. Longer flights, especially to altitudes of and above, carry a greater risk of altitude DCS.

- underwater diving before flying – divers who ascend to altitude soon after a dive increase their risk of developing DCS even if the dive itself was within the dive table safe limits. Dive tables make provisions for post-dive time at surface level before flying to allow any residual excess nitrogen to outgas. However, the pressure maintained inside even a pressurized aircraft may be as low as the pressure equivalent to an altitude of above sea level. Therefore, the assumption that the dive table surface interval occurs at normal atmospheric pressure is invalidated by flying during that surface interval, and an otherwise-safe dive may then exceed the dive table limits.

- diving before travelling to altitude – DCS can occur without flying if the person moves to a high-altitude location on land immediately after diving, for example, scuba divers in Eritrea who drive from the coast to the Asmara plateau at increase their risk of DCS.

- diving at altitude – diving in water whose surface altitude is above — for example, Lake Titicaca is at — without using versions of decompression tables or dive computers that are modified for high-altitude.

Barotrauma is injury caused by pressure effects on gas spaces. This may occur during ascent or descent. The ears are the most commonly affected body part. The most serious injury is lung barotrauma, which can result in pneumothorax, pneumomediastinum, pneumopericardium, subcutaneous emphysema, and arterial gas embolism. All divers, commercial air travelers, people traveling overland between different altitudes, and people who work in pressurized environments have had to deal with some degree of barotrauma effect upon their ears, sinuses, and other air spaces. At the most extreme, barotrauma can cause ruptured eardrums, bleeding sinuses, exploding tooth cavities, and the lung injuries described above. This is the reason why divers follow a procedure of not holding their breath during ascent. By breathing continuously, they keep the airways open and avoid pressure differences between their lungs and ambient pressure.

Although the occurrence of DCS is not easily predictable, many predisposing factors are known. They may be considered as either environmental or individual.

Decompression sickness and arterial gas embolism in recreational diving are associated with certain demographic, environmental, and dive style factors. A statistical study published in 2005 tested potential risk factors: age, gender, body mass index, smoking, asthma, diabetes, cardiovascular disease, previous decompression illness, years since certification, dives in the last year, number of diving days, number of dives in a repetitive series, last dive depth, nitrox use, and drysuit use. No significant associations with risk of decompression sickness or arterial gas embolism were found for asthma, diabetes, cardiovascular disease, smoking, or body mass index. Increased depth, previous DCI, larger number of consecutive days diving, and being male were associated with higher risk for decompression sickness and arterial gas embolism. Nitrox and drysuit use, greater frequency of diving in the past year, increasing age, and years since certification were associated with lower risk, possibly as indicators of more extensive training and experience.

High pressure nervous syndrome is rarely of importance to recreational divers. Breathing any gas at great depths (hundreds of feet) can cause seizures. Interestingly it was discovered because divers were using gas mixtures without nitrogen to be able to go to great depths without experiencing nitrogen narcosis. It turns out that nitrogen prevents HPNS. The answer? Add very small amounts of nitrogen to gas mixes when diving at great depth, small enough to avoid nitrogen narcosis, but sufficient to prevent HPNS.