Scuba diving exposes the human body to a unique environment, causing physiological stress due to significant changes in ambient pressure. While most healthy individuals can safely enjoy the underwater world, certain pre-existing medical conditions or temporary physical states can dramatically increase the risk of serious injury or sudden incapacitation. Understanding these contraindications is a matter of personal safety, as diving requires the body to efficiently manage pressure changes and gas absorption. This information does not replace the mandatory medical clearance that should be obtained from a physician with expertise in diving medicine.
Systemic Medical Contraindications
Chronic diseases affecting the circulatory system present a significant hazard. Uncontrolled hypertension, or high blood pressure, is a major concern because it increases the risk of a sudden stroke or heart attack, which is often fatal underwater. Immersion shifts blood volume toward the body’s core, forcing the heart to work against higher resistance, a stress a compromised cardiovascular system may not tolerate.
Individuals with a history of heart attack, coronary artery disease, or serious heart rhythm abnormalities (arrhythmias) face an elevated risk of sudden incapacitation. An acute cardiac event not only endangers the diver’s own life but also the life of their dive buddy. The physical exertion of swimming against a current or managing an emergency can trigger these events, especially if the underlying condition is poorly managed.
Conditions that compromise the respiratory system carry the distinct danger of pulmonary barotrauma, or lung overexpansion injury. This occurs when air becomes trapped in the lungs and expands rapidly during ascent, potentially rupturing lung tissue. Moderate to severe asthma (especially exercise- or cold-induced) and chronic obstructive pulmonary disease (COPD) are serious contraindications because they reduce the lungs’ ability to efficiently vent air.
A history of spontaneous pneumothorax, or collapsed lung, also significantly elevates the risk of barotrauma due to potential structural weaknesses in the lung tissue. When a lung ruptures during ascent, air can escape into the chest cavity, causing a pneumothorax, or into the arterial bloodstream, leading to a life-threatening arterial gas embolism (AGE). These air bubbles can travel to the brain, causing symptoms similar to a stroke.
Neurological conditions that involve a risk of sudden loss of consciousness are contraindications. Uncontrolled epilepsy or a history of recurrent seizures is a prime example, as a seizure underwater carries an extremely high risk of fatal drowning. The diving environment, with factors like oxygen toxicity at depth, sensory deprivation, and stress, can lower the seizure threshold in susceptible individuals.
Individuals with a history of epilepsy, even if seizure-free for many years, must undergo extensive evaluation by a diving medicine specialist. Furthermore, certain types of strokes or neurological conditions resulting in a significant deficit can impair a diver’s ability to safely manage equipment or respond to an emergency.
Temporary Conditions Requiring Postponement
Acute illnesses involving the upper respiratory tract, such as a severe cold, flu, or sinusitis, are temporary contraindications. Congestion blocks the narrow passages connecting the middle ear and sinuses, preventing the necessary process of pressure equalization.
If a diver cannot equalize pressure during descent, the resulting imbalance can cause severe pain, perforated eardrums, or bloody sinus discharge. A “reverse block” is also a danger, where swelling prevents expanding air from exiting during ascent, causing injury as the diver rises toward the surface.
Following major surgery, diving too soon can lead to serious complications. Abdominal surgery typically requires a minimum waiting period of six to twelve weeks to ensure internal wounds and muscle layers are fully healed. Diving before this can risk wound dehiscence or the formation of an incisional hernia due to the physical strain of carrying gear or swimming.
Chest or lung surgeries, such as those to remove lung tissue, require even longer recovery times, often six to twelve months, to ensure no residual air is trapped within the chest cavity. Any trapped air can expand dramatically on ascent, leading to a recurrence of a collapsed lung or an arterial gas embolism. For any major procedure, a clearance from the operating surgeon and a dive medicine specialist is essential.
Pregnancy is a temporary contraindication for scuba diving due to the potentially serious risk to the developing fetus. The primary concern is fetal decompression sickness, as the fetal circulatory system lacks the lung filtration mechanism that efficiently removes nitrogen bubbles. Animal studies show that gas bubbles can form in the fetal circulation even when the mother shows no symptoms. The risk is amplified because the developing fetus cannot efficiently off-gas nitrogen that has crossed the placenta back into the maternal bloodstream. All major diving organizations advise against diving during any stage of pregnancy.
Essential Physical and Sensory Prerequisites
The ability to equalize pressure in the middle ear and sinuses is necessary for safe diving. Chronic conditions like severe structural deformities of the nasal passages, chronic sinusitis, or eustachian tube dysfunction can make equalization difficult or impossible. If a person cannot achieve pressure balance, the pain and potential tissue damage from barotrauma will prevent them from safely descending.
Individuals with a perforated eardrum or who have undergone certain middle ear surgeries, such as a stapedectomy, are typically advised against diving permanently. A hole in the eardrum allows cold water to enter the middle ear, which can cause sudden vertigo and disorientation, leading to panic and a high risk of drowning.
A basic level of physical fitness and mobility is necessary for safety. Severe obesity or significant mobility issues that prevent a diver from managing heavy gear, swimming against a mild current, or performing an emergency entry/exit are contraindications. Divers must be able to perform these strenuous tasks without becoming exhausted or placing undue strain on their cardiovascular system.
Age is a factor primarily because the risk of cardiac-related death while diving increases significantly for those over 50. Older divers must be particularly vigilant about regular cardiovascular screening, as the cumulative effects of aging, such as reduced lung elasticity and increased risk of atherosclerosis, can lead to sudden cardiac events underwater.
Any person considering diving, regardless of age, should be completely honest on medical questionnaires and obtain a fitness-to-dive clearance from a physician specializing in hyperbaric or dive medicine.