Every diver hears about two things early on: nitrogen narcosis and “the bends.” And most divers carry around a slightly fuzzy, slightly scary idea of both — something about going loopy at depth, and something about bubbles in your blood. The reality is more understandable, and more manageable, than the myths suggest.
So here’s a calm, clear explainer of diving’s two big physiological risks: what actually causes each, and how divers stay well ahead of them. Knowing this stuff doesn’t just tick a box — it genuinely makes you a safer, more relaxed diver.
Nitrogen narcosis: the ‘martini effect’
Under the increased pressure of depth, the gases you breathe — nitrogen chief among them — start to have a mild anaesthetic effect on your body. The result is nitrogen narcosis, sometimes called “the narcs” or the “martini effect,” because it feels a bit like having a drink or two: a pleasant fuzziness, slowed thinking, sometimes over-confidence or, less often, anxiety.
The important, reassuring facts about narcosis are these. It generally becomes noticeable as you go deeper, and it varies from diver to diver and even day to day. Crucially, it is reversible — ascend a little, and it lifts, usually within moments, with no lasting effect. The risk isn’t the fuzziness itself so much as the impaired judgement it brings, which is why divers manage it rather than ignore it.
How do you manage it? Stay aware of your depth and how you feel, dive within the depth limits of your training, and if you notice the narcosis affecting you, simply ascend a few metres until your head clears. Experience helps too — divers learn to recognise their own early signs. And this is one of the reasons technical divers use different gas blends (adding helium) for deep dives: to reduce the narcotic load. For recreational depths, awareness and sensible limits are the tools.
Decompression sickness: why we ascend slowly
The second risk, decompression sickness (DCS, or “the bends”), works differently. While you’re at depth under pressure, your body absorbs inert gas (again mostly nitrogen) into its tissues, dissolved harmlessly. The issue is what happens on the way up. If you ascend too fast, or stay too long and too deep without managing it, that dissolved gas can come out of solution as bubbles — a bit like the fizz when you crack open a shaken bottle — and those bubbles can cause problems ranging from joint pain to serious symptoms.
The good news is that DCS is very well understood and, with sensible diving, very avoidable. The entire structure of recreational diving is built to prevent it: no-decompression limits that cap how long you stay at a given depth, slow ascents so the gas comes off gently, and a safety stop near the end of the dive to let your body offload more before you surface. Your dive computer tracks all of this continuously and keeps you within safe limits — it’s doing this maths the whole dive.
How divers stay ahead of both
Put together, the everyday habits that manage these risks are straightforward and become second nature. Dive within your training and your limits. Let your computer or tables guide your depth and time, and respect the no-decompression limit. Ascend slowly — slower than feels necessary — and make your safety stop. Dive conservatively rather than pushing every limit at once. And look after the general factors that influence your susceptibility: hydration, rest, fitness, and not overexerting. There’s also a waiting period before flying after diving, to let your body finish offloading gas — worth planning trips around.
None of this is exotic. It’s the ordinary, sensible practice that good training instils, and it’s why millions of dives happen safely. These risks aren’t random bad luck that strikes without warning — they’re understood, predictable, and managed by the way we’re taught to dive.
Knowledge is the best safety gear
The divers who handle these risks best are the ones who understand them — not the ones who worry about them vaguely, and not the ones who ignore them entirely. A solid grasp of why we ascend slowly, why we respect depth, and how our bodies handle pressure turns a scary abstraction into simple, confident practice.
If you want to understand this properly — and every diver should — it’s built into good training from the start and goes deeper as you progress. Take a look at what we teach and how we think about diving well. This article is a general overview, not medical advice; for questions about your own health and fitness to dive, talk to a physician trained in dive medicine.
Understand the risks, respect them, and they stop being scary. That’s the whole point of learning them.