Drowning is a type of suffocation induced by the submersion of the mouth and nose in a liquid. Most instances of fatal drowning occur alone or in situations where others present are either unaware of the victims situation or unable to offer assistance. After successful resuscitation, drowning victims may experience breathing problems, vomiting, confusion, or unconsciousness. Occasionally, victims may not begin experiencing these symptoms until several hours after they are rescued. An incident of drowning can also cause further complications for victims due to low body temperature, aspiration of vomit, or acute respiratory distress syndrome (respiratory failure from lung inflammation). Drowning is more likely to happen when spending extended periods of time near large bodies of water. Risk factors for drowning include  alcohol use, drug use, epilepsy, low socioeconomic status (which is often accompanied by diminished or non-existent swimming skills), lack of training and, in the case of children, a lack of supervision. Common drowning locations include natural and man-made bodies of water, bathtubs, and swimming pools.Drowning occurs when an individual spends too much time with their nose and mouth submerged in a liquid to the point of being unable to breathe. If this is not followed by an exit to the surface, low oxygen levels and excess carbon dioxide in the blood trigger a neurological state of breathing emergency, which results in increased physical distress and occasional contractions of the vocal folds.
During an apnea, the oxygen in the body is used by the cells and excreted as carbon dioxide. Thus, the level of oxygen in the blood decreases, and the level of carbon dioxide increases. Increasing carbon dioxide levels lead to a stronger and stronger breathing reflex, up to the breath-hold breakpoint, at which the person can no longer voluntarily hold his or her breath. This typically occurs at an arterial partial pressure of carbon dioxide of 55 mm Hg but may differ significantly between people. The breath-hold breakpoint can be suppressed or delayed, either intentionally or unintentionally. Hyperventilation before any dive, deep or shallow, flushes out carbon dioxide in the blood resulting in a dive commencing with an abnormally low carbon dioxide level; a potentially dangerous condition known as hypocapnia. The level of carbon dioxide in the blood after hyperventilation may then be insufficient to trigger the breathing reflex later in the dive. Following this, a blackout may occur before the diver feels an urgent need to breathe. This can occur at any depth and is common in distance breath-hold divers in swimming pools. Both deep and distance free divers often use hyperventilation to flush out carbon dioxide from the lungs to suppress the breathing reflex for longer. It is important not to mistake this for an attempt to increase the bodys oxygen store. The body at rest is fully oxygenated by normal breathing and cannot take on any more.