Everything You Knew About DCS (Decompression Sickness) Just Got More Complicated

New Research Has Some Surprising Answers

Based on peer-reviewed research published in International Maritime Health, 2026

Studies Referenced in This Article

Study 1: Marroni A, Kot J, Pieri M, Pelliccia R, Balestra C. "Identification of DCS risk factors in recreational diving: multifactorial model based on the DAN DSL Database 2024." International Maritime Health 2026; 77(1): 1-12. DOI: 10.5603/imh.108038

Study 2: Marroni A, Pieri M, Imbert JP, Pelliccia R, Arena M, Marroni L, Germonpre P, Cialoni D, Balestra C. "Deep versus shallow decompression stops: illustration of different decompression strategies used in technical diving." International Maritime Health 2026. DOI: 10.5603/imh.106791

Both studies are from the DAN Europe Research Division and are published open access under CC BY-NC-ND 4.0.

First, a Quick Refresher on DCS

When you dive, your body absorbs nitrogen under pressure. The deeper you go and the longer you stay, the more nitrogen dissolves into your tissues and bloodstream. Ascend too fast, and that nitrogen can form bubbles inside your body before it has a chance to exit safely through your lungs.

Those bubbles are decompression sickness, or DCS. Divers call it the bends. Symptoms can range from skin rashes and joint pain all the way to paralysis and death. It is not common, but it is serious, and it can happen even when you think you did everything right.

DCS can strike even when a diver follows their computer or tables perfectly. So researchers have been asking a deeper question: beyond the obvious rules, what actually tips the balance toward getting bent?

Two new studies from the DAN Europe research team, published in the International Maritime Health journal in 2026, go a long way toward answering that.

Study 1: The Biggest Dive Database Ever Analysed

Full title: "Identification of DCS risk factors in recreational diving: multifactorial model based on the DAN DSL Database 2024" | Marroni et al., Int Marit Health 2026; 77(1): 1-12

The first study is remarkable simply for its size. Researchers analysed 127,957 dives from 5,907 divers recorded in the DAN Europe database. This is real-world data from real recreational divers, not a controlled lab experiment. That matters, because it means the findings reflect how actual divers actually dive.

Out of those 127,957 dives, decompression sickness was reported in 628, giving an overall incidence rate of 0.49%. Less than half a percent sounds small, but scaled across the millions of dives made globally every year, it represents a very large number of people getting hurt.

The researchers built a statistical model to identify which factors independently predicted whether a diver got DCS. They found 12.

The 12 Risk Factors, Explained Simply

1. How Saturated Your Tissues Are When You Surface

This was the single biggest predictor of DCS, and it is the one most directly under your control.

The researchers used a measure called the DAN Surface Supersaturation Gradient (DSSG). This is essentially a number that tells you how loaded your body's tissues are with dissolved gas at the moment you reach the surface. The higher the number, the more gas is still dissolved, and the more likely it is to form bubbles.

Divers who got DCS had a significantly higher DSSG than those who did not. When the DSSG exceeded 1.0, a staggering 37.5% of dives resulted in DCS. Below 0.7, the rate was nearly zero.

Practical takeaway: Ascend slowly. Do your safety stops. Never skip the three-minute stop at five metres. If your computer tells you to slow down, listen to it. The DSSG is what your ascent profile directly controls.

2. Which Tissue Compartment is Most Saturated

Decompression models divide the human body into 16 theoretical tissue compartments, each representing tissues that absorb and release gas at different speeds. Fast compartments include blood and some organs. Slow compartments include fat and connective tissue. The study found that which compartment is most saturated when you surface also independently affects DCS risk. This connects directly to the second study, covered below.

3. Being Female (Odds Ratio: 4.63x)

This is one of the most striking findings in the study. In the raw data, DCS occurred in 1.25% of dives by female divers, compared to 0.38% of dives by male divers. After the researchers controlled for every other variable, being female was still independently associated with 4.63 times greater odds of DCS.

This does not mean women should not dive. It means the diving and medical community needs to pay far more attention to gender differences in decompression physiology. Animal studies suggest differences in inflammation response, blood clotting, and bubble formation between males and females. This area warrants serious further research.

4. BMI (Body Mass Index)

DCS risk followed a U-shaped curve based on BMI. Both very underweight and very obese divers showed higher risk, while those in the normal-to-overweight range had lower risk. In the multivariate analysis, a lower BMI class was associated with about a 15% increase in DCS odds per class below normal.

5. Number of Repetitive Dives (Protective)

Each additional dive in a series reduced DCS odds by about 6%. The researchers believe this is connected to the extension of surface intervals between dives, and possibly to a depletion of the microscopic bubble nuclei that act as starting points for gas bubble formation. More dives over a period means these nuclei gradually get used up.

6. Surface Interval (Protective)

Each additional hour spent at the surface before a subsequent dive reduced DCS odds by 4%. Simple takeaway: wait longer between dives. The longer you wait, the more nitrogen your body offgasses safely.

Practical takeaway: Extend your surface intervals wherever possible, especially on multi-dive days. Rushing back into the water increases your risk measurably.

7. Number of Gas Mixtures Used (Odds Ratio: 2.87x)

Using more than one breathing gas during a dive nearly tripled DCS odds. This largely reflects technical diving, which typically involves greater depths, more complex profiles, and gas switches. It is not the gases themselves that cause the problem, but everything that comes with that style of diving.

8, 9, 10. Exercise, Thermal Comfort, and Workload

Important note on data quality: The findings for exercise before diving, thermal comfort during the dive, and workload during the dive are all based on self-reported, subjective questionnaire responses from divers. These are not objectively measured variables. One diver's "light exercise" is another's "moderate." One diver's "comfortable" temperature is another's "cold." These responses cannot be verified against any objective measurement. The associations found here are genuine starting points for further investigation, but they should not be treated as established facts until confirmed by studies using objective, measured data. They tell us where to look, not what is definitively true.

With that caveat clearly stated, here is what the data showed:

• Exercise before diving was associated with double the DCS risk in the multivariate analysis (Odds Ratio: 2.06). However, other research has shown that specific, controlled pre-dive exercise, sometimes called preconditioning, is actually protective. The database could not distinguish between the two. This finding is unresolved and requires proper controlled study with objective exercise measurement.
  

• Thermal comfort during the dive showed a counterintuitive result: feeling warm was associated with higher DCS risk (Odds Ratio: 2.83) compared to feeling cold. At first glance this seems to contradict common sense. But "feeling warm" and "being warm" are not the same thing. We have written previously about how divers consistently underestimate heat loss underwater, often feeling comfortable at the surface while their core temperature is already dropping at depth. Read: "You Are Getting Cold. You Just Don't Know It Yet" at proscuba.in. That piece does not contradict this finding. If anything, it adds a layer to it: a diver reporting thermal comfort may already be losing heat they simply cannot detect. There is also a simpler behavioural explanation worth considering: a diver who felt cold may have cut their dive short, reduced their depth, or ascended more conservatively, all of which would naturally lower their DSSG and reduce DCS risk. The data cannot distinguish between these possibilities. Whether the mechanism is physiological, behavioural, or both remains an open question that needs objective temperature measurement and dive profile correlation to answer properly.
  

• Workload during the dive increased DCS odds by 61% (Odds Ratio: 1.61). Physical effort underwater increases gas uptake. This is consistent with established physiology, but the actual intensity of workload was not measured.

11. Technical Dive Purpose (Odds Ratio: 1.36x)

Technical dives had a DCS rate of 1.24% compared to 0.57% for recreational dives. Diving for technical purposes independently increased DCS odds by 36%. Again, this reflects the greater complexity and depth exposure associated with technical diving.

12. Feeling Tired Before the Dive (Protective, Odds Ratio: 0.30)

This is another self-reported variable and must be interpreted with caution. The finding that tired divers had lower DCS rates is interesting, but the mechanism is based on speculation. It cannot be confirmed without objective measurements of fatigue, and the strong negative correlation between exercise and tiredness in the data suggests these two variables are intertwined in ways the questionnaire cannot unpick.

The data showed that divers who reported feeling tired or exhausted before diving had lower DCS rates (0.29%) than rested divers (0.51%), with fatigue reducing DCS odds by 70% in the model. The most plausible explanation is behavioural: tired divers may ascend more slowly, stay shallower, cut dives short, and generally act more conservatively. This would reduce their DSSG and therefore their DCS risk. But this remains speculative without objective data on ascent profiles correlated with reported fatigue.

Study 2: Deep Stops vs. Shallow Stops

Full title: "Deep versus shallow decompression stops: illustration of different decompression strategies used in technical diving" | Marroni et al., Int Marit Health 2026. DOI: 10.5603/imh.106791

The second study is smaller and more focused. It asked a specific practical question: when coming up from a technical dive, is it safer to stop at deeper depths first, or shallower depths first? Both take exactly the same total time. Only the distribution of that time differs.

The Setup

18 experienced technical divers (certified diving instructors) each performed two standardised dives in a controlled pool environment. Both dives were to 40 metres for 40 minutes, using trimix (21% oxygen, 35% helium, balance nitrogen) on the bottom and high-oxygen nitrox on the ascent. Total decompression time was identical for both profiles: 38 minutes.

The Two Profiles

• DEEP profile: First stop at 21 metres, then 18, 15, 12, 9, 6, and 3 metres. About one third of decompression time spent deeper, two thirds shallower.
  

• SHALLOW profile: First stop at only 9 metres, then 6 and 3 metres only. Almost all decompression time spent close to the surface.

What They Measured

Using echocardiography (ultrasound imaging of the heart), researchers counted gas bubbles circulating in the divers' bloodstream after each dive. This is the gold standard method for measuring decompression stress. More bubbles equals more stress equals higher DCS risk. Measurements were taken every 15 minutes for 90 minutes after surfacing.

What They Found

The deep stop approach was clearly better. Average bubble counts were significantly lower after the DEEP procedure (6.7 bubbles per heartbeat) compared to the SHALLOW procedure (10.7 bubbles per heartbeat). That is a highly statistically significant difference.

More importantly: three cases of cutis marmorata, a skin manifestation of DCS, occurred after the SHALLOW profile. Zero DCS cases occurred after the DEEP profile. The three affected divers all had more than 40 bubbles per heartbeat. All recovered fully after 60 minutes of pure oxygen breathing.

Key finding: Same total decompression time. Same divers. Same depth and gas. Different stop distribution. The deep-first approach produced significantly fewer bubbles and zero DCS cases versus three in the shallow group.

Why Does the Deep Approach Work Better?

The researchers offer three explanations:

• The oxygen window effect: When you breathe high-oxygen gas at 21 metres, where oxygen pressure is relatively high, your body uses that oxygen metabolically. This creates a biological vacuum of sorts, pulling dissolved inert gas out of bubbles faster than it can accumulate. Bubbles dissolve before they grow large enough to cause problems.
  

• More time on high oxygen at depth: The deep profile allowed divers to breathe nitrox 50 starting at 21 metres, where oxygen partial pressure is 1.55 bar. This aggressively accelerates nitrogen removal from tissues at the most critical phase of the ascent.
  

• Better gas distribution between tissue types: Fast tissues desaturate more completely during the deeper stops, which prevents them from later contributing to bubble growth during the shallower portion of the ascent.

An Important Caveat on Sample Size

This study involved only 18 divers. While the results are statistically significant and the methodology is sound, the small sample size means we should view this as strong preliminary evidence rather than a definitive conclusion. The researchers themselves acknowledge this limitation. Larger studies are needed to confirm these findings across a broader population of divers.

How the Two Studies Connect

Read together, these studies tell a coherent story.

The first study, with its nearly 128,000 dives, tells us that the single most important modifiable factor in DCS risk is the supersaturation gradient when you surface. The lower it is, the safer you are. Everything about how you ascend, how slowly you go, how long your stops are, how long you wait between dives, feeds directly into that number.

The second study then shows, in a controlled setting, that how you distribute your decompression time matters enormously, even when the total time is the same. Starting deeper and working your way up, particularly when breathing high-oxygen gas, appears to produce meaningfully lower bubble loads and fewer DCS events.

Together they point toward the same conclusion: the quality and distribution of your ascent, not just the raw numbers your dive computer shows, is central to staying safe.

A Note on Subjective Data: When "Feelings" Are Not Enough

Several of the variables in the first study deserve special attention because they are based entirely on how divers described their own experience rather than on any objective measurement. These include:

• Feeling before the dive: rested, tired, or exhausted
  

• Thermal comfort during the dive: comfortable, cold, very cold, or hot
  

• Exercise before diving: none, light, moderate, or heavy
  

• Workload during the dive: none, light, moderate, heavy, or exhausting

These were tick-box answers on a questionnaire submitted by the diver. There was no external verification. No thermometer measured water temperature. No heart rate monitor measured exercise intensity. No objective scale measured fatigue.

This is not a criticism of the research. Collecting this kind of self-reported data at scale is genuinely difficult, and the researchers are transparent about these limitations. But it does mean that the associations found between these variables and DCS risk must be treated carefully.

Self-reported data has well-documented problems in research:

• Two people exercising at the same intensity will describe it very differently depending on their fitness levels.
  

• Divers may unconsciously under-report alcohol use, fatigue, or workload, especially if they feel they should not have dived in those conditions.
  

• The meaning of "comfortable" temperature varies enormously between individuals.
  

• Variables interact in ways the questionnaire cannot capture: a diver who is tired because they exercised heavily is reporting two things that are deeply intertwined.

What does this mean in practice? The associations with subjective variables, exercise, thermal comfort, workload, and pre-dive feeling, are real statistical signals worth taking seriously. But they are starting points for further research, not established facts. Before any of these findings can be translated into firm dive safety advice, they need to be confirmed by studies that measure these variables objectively. Until then, treat them as hypotheses rather than conclusions.

The findings based on hard, objectively measured data, particularly DSSG and gender, are on far firmer ground and deserve more weight in practical decision-making.

What This Means for You as a Diver

Here is the practical summary of what these two studies, taken together, mean for recreational and technical divers:

Things That Are Clearly Evidence-Based

• Ascend slowly and always complete your safety stops. This directly reduces your DSSG, the single strongest predictor of DCS.
  

• Extend your surface intervals. Every hour at the surface reduces DCS odds by 4%.
  

• If you are a female diver, discuss this research with your dive medical professional. The gender difference in DCS risk is large and not yet fully understood.
  

• Be extra cautious if your BMI is significantly below or above the normal range.
  

• Technical diving carries meaningfully higher DCS risk. Ensure your training, planning, and gas management reflect that.
  

• If you are planning decompression dives, deep stops using high-oxygen decompression gas appear to produce lower bubble loads than shallow-only profiles with the same total decompression time.

Things Worth Being Mindful Of (But Not Yet Proven)

• How you feel before a dive may influence how you dive, and therefore your risk. If you feel genuinely unwell, that is a reason to sit out.
  

• Thermal exposure during a dive may affect decompression, but the relationship is not straightforward. A diver who felt cold may simply have dived more conservatively, cutting the dive shorter or ascending earlier, which would naturally reduce their DCS risk regardless of temperature. Whether warmth itself is a physiological risk factor, or whether reported comfort reflects a diver who pushed their profile further, requires objective measurement to untangle. Do not read this as "stay cold to stay safe." Read it as "we do not fully understand this yet."
  

• Heavy physical workload underwater appears to increase risk. Avoid unnecessary exertion, especially during ascent.
  

• Pre-dive exercise is complicated. Casual heavy exercise may increase risk. Specific controlled preconditioning exercise may be protective. Until more is known, moderate, deliberate activity rather than exhausting effort seems prudent before diving.

The Bigger Picture

What makes these two studies significant is not any single finding but what they represent as a body of work. DAN Europe has been collecting real-world diving data since 1993, and the database they are now analysing, nearly 128,000 dives, is the largest of its kind in existence. The findings are not from a laboratory with idealised conditions. They are from the actual ocean, with real divers making real decisions.

That means the conclusions, where they rest on objective data, reflect the reality of diving rather than a controlled approximation of it. And the direction they point is consistent and clear: how you ascend matters more than almost anything else. Take it slow, give yourself time, breathe the right gas at the right depth, and respect the physiology that your dive computer can only approximate.

The bends is not random. It has causes. And we are getting better at understanding them.