A surprisingly wide range of medical conditions can disqualify you from scuba diving or require careful medical clearance before you get in the water. The underwater environment imposes stresses on the body that most people never encounter on land, including elevated pressure on the lungs and sinuses, shifts in blood volume toward the chest, and exposure to breathing gases at concentrations that change with depth. Conditions that are perfectly manageable in everyday life can become dangerous or even fatal at depth, which is why dive medicine takes a broader and more cautious view of fitness than most recreational sports.
Heart and Circulatory Problems
Cardiovascular disease is one of the leading contributors to scuba diving fatalities. A review of Divers Alert Network fatality data found significant coronary artery disease in about half of the cases examined and cardiomyopathy in roughly 60%.1Heart, Lung and Circulation. Cardiovascular Disease and SCUBA Diving Fatalities: A Review of Divers Alert Network Fatalities An Australian study of diving deaths between 2001 and 2013 attributed a quarter of fatalities to cardiac causes like ischemic heart disease and arrhythmias.2PubMed Central. Medical conditions in scuba diving fatality victims in Australia, 2001 to 2013 People with untreated or poorly controlled coronary artery disease, heart failure, certain arrhythmias, or inherited electrical disorders of the heart (channelopathies) need thorough evaluation and treatment before they can be considered safe to dive.3PubMed Central. Cardiovascular considerations for scuba divers
The reason heart disease is so dangerous underwater comes down to what immersion does to your body. When you enter the water, blood shifts from your limbs toward your chest, increasing the volume your heart has to handle. Add cold water, physical exertion, and the stress of breathing compressed gas, and you’ve created conditions that can push a compromised heart past its limits. This combination of factors is also what drives immersion pulmonary edema, a condition in which fluid leaks into the lungs during a dive. Hypertension is the cardiovascular condition most frequently associated with it.4PubMed Central. Immersion pulmonary oedema: a cardiological perspective Even divers without known heart disease can develop immersion pulmonary edema when cold water, deep dives, and hard swimming converge, though the risk is higher for people with underlying cardiac issues.5PubMed. Pulmonary oedema in healthy SCUBA divers: new physiopathological pathways
Patent Foramen Ovale
One heart-related condition that gets a lot of attention in dive medicine is a patent foramen ovale, a small flap-like opening between the upper chambers of the heart that most people never know they have. Roughly a quarter of the general population has one, and in daily life it causes no symptoms. Underwater, it becomes relevant because it can allow nitrogen bubbles formed during ascent to cross directly into the arterial bloodstream, bypassing the lungs where those bubbles would normally be filtered out. A study of 30 divers with histories of decompression sickness found that 37% had a patent foramen ovale detectable by contrast echocardiography, and among those with serious symptoms the figure rose to 61%, compared with just 5% in healthy volunteers.6PubMed. Patent foramen ovale and decompression sickness in divers Having a patent foramen ovale does not automatically disqualify you from diving, but it does increase your risk profile for decompression sickness, and many dive physicians will counsel more conservative dive profiles or, in some cases, recommend closure of the opening before continued diving.
Lung Conditions and Breathing Problems
Your lungs are the organ system most directly affected by the physics of diving. As you descend, the gas you breathe is delivered at higher pressure, and as you ascend, that gas expands. Any condition that traps air in part of the lung can prevent it from escaping during ascent, which may cause the lung tissue to rupture. This is pulmonary barotrauma, and it’s the reason several lung conditions are treated as serious red flags.
Asthma tops the list of common respiratory concerns for divers. If a diver has an asthma attack underwater, bronchospasm can obstruct the small airways and trap expanding gas. That trapped gas can overdistend the lung and cause barotrauma.7PubMed. SCUBA Diving and Asthma: Clinical Recommendations and Safety Guidelines vary by country and over time, but in general, people with well-controlled asthma who pass normal lung function tests and don’t wheeze with exercise or cold air exposure may be cleared to dive. Those with poorly controlled or exercise-induced asthma face a higher threshold for clearance and may be advised against diving entirely.
A history of spontaneous pneumothorax, where the lung collapses without an obvious external cause, is considered an absolute contraindication for diving unless a bilateral surgical pleurectomy has been performed to prevent recurrence.8PubMed Central. Recurrence of spontaneous pneumothorax six years after VATS pleurectomy: evidence for formation of neopleura The concern is straightforward: if your lung has collapsed once without a clear cause, the structural weakness that allowed it could be triggered again by the pressure changes of diving.
Lung cysts and bullae, the fluid-filled or air-filled sacs that some people develop in lung tissue, pose a similar risk. In patients with Birt-Hogg-Dubé syndrome, a genetic condition that causes lung cysts, two out of a cohort of patients developed spontaneous pneumothorax within 48 hours of shallow dives, and researchers have documented that chest CT scans revealed previously undetected cysts in roughly a third of divers who experienced pulmonary barotrauma.9PubMed Central. Recommendations on scuba diving in Birt-Hogg-Dubé syndrome Any condition that creates structural abnormalities in the lung parenchyma, including cystic fibrosis and advanced COPD, raises concerns about air trapping and potential barotrauma.
Ear, Nose, and Throat Conditions
Ear problems are by far the most common medical complaints among divers. Estimates suggest that around 80% of adult divers and 85% of young divers experience an ear, nose, or throat complaint related to diving at some point.10JAMA Network. Otorhinolaryngology and Diving—Part 1: Otorhinolaryngological Hazards Related to Compressed Gas Scuba Diving: A Review Most of these are minor and temporary, but certain conditions make diving risky or impossible.
The core issue is equalization. As you descend, the water pressure on your eardrums increases, and you need to actively push air through your eustachian tubes to equalize pressure in the middle ear. If you can’t do this, whether because of chronic sinus congestion, nasal polyps, a deviated septum, or an upper respiratory infection, the pressure difference can damage your eardrum or, worse, injure the inner ear. Inner ear barotrauma occurs when failed equalization transmits pressure changes through the oval and round windows of the inner ear, and inner ear decompression sickness involves gas bubbles forming in the blood vessels of the inner ear during ascent.11PubMed Central. Inner Ear Disorders in SCUBA Divers: A Review Both can cause hearing loss, tinnitus, and vertigo. Vertigo underwater is particularly dangerous because it causes disorientation and can lead to panic and drowning.
People with a history of ear surgery, chronic ear infections, or a perforated eardrum need clearance from an ENT specialist before diving. Conditions that chronically block the eustachian tubes or sinuses may be disqualifying if they prevent reliable equalization. Even something as temporary as a head cold is grounds to skip a dive, because the congestion can prevent equalization on descent and, if a decongestant wears off during the dive, trap air on ascent.
Epilepsy and Seizure Disorders
Epilepsy has traditionally been treated as one of the strictest contraindications for diving. The reasoning is simple: a seizure underwater almost certainly means drowning. If you lose consciousness, your regulator falls out of your mouth, and you’re unlikely to be rescued in time. In the United Kingdom, the Sport Diving Medical Committee advises that a person with epilepsy must be seizure-free and off all medication for at least five years before being considered for diving.12PubMed. Epilepsy and recreational scuba diving: an absolute contraindication or can there be exceptions? A call for discussion Other countries set similar thresholds, though the exact number of seizure-free years varies. The underlying science supports the caution: the risk of seizure recurrence decreases with time in remission, but it never reaches zero.
Some dive-medicine professionals have argued that these rules are overly conservative for people with well-characterized, low-risk seizure histories. But the consequences of being wrong are so severe that most medical guidelines err on the side of restriction. Any condition that causes episodes of loss of consciousness, including syncope (fainting), certain cardiac arrhythmias, or severe hypoglycemia, raises the same fundamental concern.
Migraines With Aura
Migraines deserve separate mention because they create a specific diagnostic problem underwater. Migraine with aura can produce neurological symptoms like visual disturbances, numbness, or speech difficulty that closely mimic the signs of decompression sickness or arterial gas embolism. When a diver surfaces with those symptoms, the immediate question is whether they need emergency treatment in a hyperbaric chamber. If the cause is actually a migraine, chamber treatment is unnecessary but not harmful. If it’s decompression sickness and it’s mistaken for a migraine, the delay can cause permanent injury. Focal neurological symptoms in a diver should be treated with 100% oxygen and referred to a hyperbaric facility without delay, even if the diver has a history of migraine.13PubMed. Headache and facial pain in scuba divers
There is also a documented connection between migraine with aura and patent foramen ovale. A case report described a young diver with known migraine with aura who developed headache with neurological symptoms during a scuba lesson and was later found to have a patent foramen ovale.14PubMed. Migraine With Neurological Features in a Scuba Diver With a Patent Foramen Ovale The combination of migraine with aura and a patent foramen ovale raises particular concern, because both independently increase diving risk and together they complicate the clinical picture further. People with frequent migraine with aura are generally advised to undergo careful evaluation before diving.
Diabetes
Diabetes used to be a blanket contraindication for diving, largely because of the risk of hypoglycemia. Low blood sugar underwater can cause confusion, loss of consciousness, and drowning in the same way a seizure can. Over the past two decades, that position has softened considerably as evidence has accumulated that divers with well-managed diabetes can participate safely with proper protocols.
Advances in glucose monitoring and insulin delivery have changed the practical risk calculation. A structured safety program in Italy tracked over 1,100 dives by people with type 1 diabetes. Participants monitored blood glucose before and after each dive, aiming for stable levels between 150 and 250 mg/dL. Post-dive hypoglycemia occurred in only about 2% of dives when the protocol was followed, and no severe episodes happened during or after diving.15PubMed. Performance of a safety protocol for scuba diving in people with type 1 diabetes: 20 years of “Diabete Sommerso®” experience Close self-monitoring, meal adjustments, and medication timing are central to safe diving with diabetes. Periodic medical evaluation remains important because the secondary complications of diabetes, including heart disease, nerve damage, and impaired wound healing, are independently relevant to dive fitness.16PubMed Central. Recreational diving in persons with type 1 and type 2 diabetes: Advancing capabilities and recommendations
Sickle Cell Trait and Other Blood Conditions
Sickle cell trait, the carrier state where a person has one copy of the sickle hemoglobin gene, is sometimes flagged as a diving concern because of a theoretical worry that the low-oxygen, high-pressure underwater environment could trigger sickling of red blood cells. A review of the literature found no reports of sickle cell trait causing dive-related injury, and the analysis suggested minimal increased risk for recreational and technical civilian diving.17Undersea and Hyperbaric Medicine. Sickle cell trait and diving: Review and recommendations Sickle cell disease itself, the full condition with two copies of the gene, is a different matter: the chronic anemia, vascular problems, and risk of sickling crises make diving much more hazardous. People with sickle cell trait who are otherwise healthy are generally considered fit to dive.
Pregnancy
Pregnant women are advised not to dive. The mother herself faces no significantly elevated risk beyond what any diver faces, but the developing fetus has no protection against decompression problems. Nitrogen bubbles that form during ascent can cross the placenta, and the fetal circulatory system, which has shunts that bypass the lungs, has no way to filter them.18Seminars in Perinatology. Diving and pregnancy Animal studies have shown possible adverse effects from fetal decompression illness and from hyperbaric oxygen exposure.19PubMed. SCUBA Diving in Pregnancy Ethical considerations make it impossible to conduct controlled human trials on this question, so the recommendation against diving during pregnancy is based on animal data and theoretical risk. Most dive organizations advise stopping as soon as pregnancy is confirmed or suspected, and waiting until after delivery and full recovery before resuming.
Medications and Diving
The medications you take can matter as much as the conditions they treat. Sedatives, strong antihistamines, and certain anti-anxiety or antidepressant drugs can impair judgment, slow reaction time, or cause drowsiness, all dangerous underwater. Some medications also interact with the elevated partial pressures of gases encountered at depth in ways that aren’t fully understood.
A systematic review of medication effects under hyperbaric conditions found that, reassuringly, human studies showed no dangerous pressure-related drug interactions. Among the useful findings: pseudoephedrine reduced ear barotrauma, and vitamins C and E reduced some physiological stress markers during diving.20PubMed Central. Systematic review on the effects of medication under hyperbaric conditions: consequences for the diver That said, the evidence base is thin. Most drugs have simply never been studied in a hyperbaric environment, and absence of evidence is not evidence of absence. The practical advice from dive physicians is to discuss all medications with a doctor experienced in dive medicine. If a medication causes drowsiness, dizziness, or impaired thinking on land, those effects are likely to be as bad or worse at depth.
Mental Health Conditions
Panic is a major contributor to diving accidents, and any mental health condition that increases the likelihood of a panic response underwater is relevant. Claustrophobia, severe anxiety disorders, and untreated panic disorder all raise concerns. The diving environment involves wearing a mask that restricts your visual field, breathing through a mechanical device, and operating in a space you cannot leave instantly. For someone prone to panic, these conditions can trigger an episode that leads to a rapid, uncontrolled ascent, bolting to the surface is a natural panic response but one that carries serious risk of lung barotrauma and decompression sickness.
Psychiatric medications add another layer. Many antidepressants and anxiolytics have side effects that overlap with symptoms of nitrogen narcosis, a state of impaired cognition that occurs at deeper depths. Separating drug side effects from narcosis can be difficult, and the combination may amplify both. People with well-managed anxiety who are comfortable in confined spaces and in water can and do dive safely, but those whose conditions are unstable or who rely on heavily sedating medications face real obstacles.
Fitness to Dive After COVID-19
The pandemic introduced a new category of fitness-to-dive concern. COVID-19 can leave persistent changes in lung tissue that affect a diver’s safety. A study of 43 divers undergoing post-COVID fitness assessments found that about 30% were temporarily restricted from diving, all due to persistent lung changes visible on CT scans. Ground-glass opacities and fibrotic changes were the most common findings. In the first three months after a COVID diagnosis, roughly 73% of divers showed at least one lung lesion on CT, a number that dropped to about 19% at later follow-ups.21PubMed Central. Post COVID-19 fitness to dive assessment findings in occupational and recreational divers The concern with persistent lung lesions is the same air-trapping risk that applies to cysts and bullae: if an area of damaged lung tissue cannot equalize pressure during ascent, barotrauma can result.
Most dive medicine organizations recommend waiting at least a few months after a symptomatic COVID-19 infection before diving and undergoing lung function testing or imaging if symptoms like shortness of breath or reduced exercise tolerance persist. This guidance has evolved as more data have accumulated, and the waiting periods have generally shortened compared with early pandemic recommendations for people who had mild illness and recovered fully.
The Medical Screening Process
Before your first dive course, you’ll fill out a medical questionnaire. Most training agencies use the Recreational Scuba Training Council (RSTC) form, which asks about a long list of conditions from heart disease to psychiatric illness. A study of the RSTC form’s effectiveness in Hong Kong found that less than a third of prospective divers answered “all negative” to the health questions, and about 15% had difficulty understanding or completing the form.22Diving and Hyperbaric Medicine. The usefulness of the RSTC medical questionnaire in pre-participation health risk assessment of recreational scuba divers in Hong Kong A positive answer to any question doesn’t automatically disqualify you but does trigger a requirement for physician clearance, ideally from a doctor with training in dive medicine.
The screening process works on a spectrum. Some conditions are considered absolute contraindications, meaning they disqualify you under essentially all circumstances. These include untreated pneumothorax, active psychosis, and severe, unstable heart or lung disease. A larger group of conditions are relative contraindications: they require evaluation, and the decision depends on severity, stability, and how well the condition is managed. Diabetes, well-controlled asthma, and a repaired patent foramen ovale all fall into this category. Physicians weigh the specific details of your case, including the type of diving you plan to do, because a shallow warm-water reef dive presents different physiological demands than a deep cold-water technical dive.
Bone Health and Long-Term Divers
One condition that most recreational divers never think about is dysbaric osteonecrosis, a deterioration of bone tissue caused by repeated pressure exposure. The frequency, duration, and depth of pressure exposure, inadequate decompression, prior episodes of decompression sickness, and increasing age have all been associated with its development.23PubMed Central. Dysbaric osteonecrosis in technical divers: The new ‘at-risk’ group? Historically associated with commercial divers and caisson workers, it has also been identified in technical divers who push depth and time limits. When it occurs near a joint surface, it can cause painful collapse of the bone and may require joint replacement. For the average recreational diver doing a couple of reef dives a year, this is not a meaningful concern. For someone doing frequent deep or decompression diving over many years, it’s worth knowing about, and it’s one more reason that conservative dive profiles and adequate surface intervals matter over a long diving career.