On days of intense heat, a swim in the cold sea is one of the main solutions to mitigate the impacts of high temperatures. But are there risks to such a sudden change when you leave a thermal sensation of up to 40ºC and enter water often below 18ºC? GLOBO spoke with experts who clarified the myths and truths on the subject.
Is there a risk of thermal shock?
Cardiologist, professor at the State University of Bahia (Uneb) and president of the Brazilian Society of Cardiac Arrhythmia (Sobrac), Alexsandro Fagundes, explains that yes, there is a risk of sudden change in body temperature when entering the freezing sea on very hot days:
— Thermal shock is a set of changes that can occur in the body when exposed to a sudden change in body temperature. This is likely to occur when entering cold water directly on a day of very high heat exposure, with a thermal sensation above 40ºC, particularly in the Southeastern states, where seawater temperatures tend to be colder.
What are the signs of thermal shock?
— The risks of this very abrupt change from falling directly into cold water are vasoconstriction and the reactive changes that cold promotes in the body. This vasoconstriction can impair the perfusion of noble organs, mainly the brain, leading to hypotension, muscle tremors, a feeling of fainting, dizziness and possibly even a risk of drowning in a very extreme case — explains Fagundes.
Vasoconstriction is a reduction in blood vessel diameter, i.e. narrowing, and occurs in response to abrupt exposure to lower temperatures as a physiological mechanism to prevent heat loss. However, this increases the body’s blood pressure, which can impair perfusion (blood flow) in important organs, as the cardiologist explains.
Does wetting any part of your body before going in help? Or can you dive straight in?
Fagundes says yes, there are precautions that can be taken to avoid the risk of thermal shock on days of intense heat, and one of them is to wet certain parts of the body before diving so that the body does not experience a sudden change in temperature:
— It is important to ensure that this temperature variation occurs gradually. It’s worth wetting your body little by little. And staying well hydrated also helps avoid this complication. In addition, never enter the water in unsupervised places, without anyone nearby, that is, without the possibility of help if something happens to you in the sea.
Are children and the elderly more vulnerable to dehydration?
Marcelo Franken, cardiologist at the Israelita Albert Einstein Hospital, in São Paulo, also emphasizes the importance of being well hydrated on days of intense heat and explains that the loss of fluids also affects the body’s blood pressure.
— The human body tends to maintain a constant temperature between 36ºC and 37ºC. When temperatures rise, the body triggers cooling mechanisms, such as sweating, which in excess, without adequate fluid replacement, can lead to dehydration – he explains and continues:
— Dehydration leads to a decrease in blood pressure, a loss of the body’s ability to transport blood with nutrients to all tissues, and changes in electrolytes in the blood. This can lead to drowsiness, mental confusion, fainting and, in more severe cases, arrhythmias, kidney failure, stroke and heart attack.
In this context, the expert affirms that yes, children and the elderly are more vulnerable to dehydration scenarios: — Elderly people are less thirsty and often do not have the initiative to drink water, young children will also only replace fluid losses if offered. Additionally, people with chronic illnesses live in a fragile balance, with few reserves, and intense heat can cause an imbalance.
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