The therapeutic use of sunbathing for strengthening the body—known as heliotherapy—has been recognized since ancient times. In Ancient Greece and Rome, sunbathing was a common part of daily wellness routines. Special rooms or sun terraces were created in baths and even on rooftops for this purpose. During the Middle Ages, the medicinal use of sunlight was severely limited, but the physician Avicenna noted in his writings that sunlight could protect against diseases. Today, scientists have thoroughly studied the significance of solar radiation for the human body, establishing a connection between the effects of sunlight and its spectral composition. The body’s reaction to infrared (with wavelengths of 760–2300 micrometers), visible (400–760 micrometers), and ultraviolet (295–400 micrometers) rays varies significantly.
Exposure to infrared sunlight raises tissue temperature. The complex biological effects of ultraviolet rays include their bactericidal action, the formation of calciferol (vitamin D), and characteristic skin reactions such as redness and pigmentation. The impact of ultraviolet radiation depends on the wavelength of the emitted rays.
Proper use of sunlight can help strengthen the body, while improper exposure can be harmful to health, primarily causing sunburn or heatstroke. Therefore, it is crucial to understand how sunlight affects the body based on the duration of exposure, the season, and local conditions.
Any rays within the solar spectrum (infrared, visible, and ultraviolet) can cause skin burns, but sunburns most commonly result from excessive absorption of the shortest rays—ultraviolet rays.
In the mildest form of sunburn, the skin reddens due to prolonged dilation of capillaries. In more severe cases, the upper layers of skin peel away, and blisters form, which later burst. Excessive exposure to ultraviolet rays can lead to necrosis of skin areas. If the burn covers large areas of the body, it can cause an increase in body temperature and nausea.
In cases of intense and prolonged exposure to solar radiation, especially without adequate protection for the head from direct sunlight, heatstroke can occur. Those affected by heatstroke require immediate medical attention.
When a person is sunbathing, not only direct sunlight affects the body, but also scattered and reflected rays. Scattered light is created when sunlight is diffused by air molecules, dust particles, and microscopic water droplets. The shorter the wavelength of the rays, the more they scatter. For instance, ultraviolet rays scatter more than visible rays. Scattered light can reach significant intensity, which is why gradual and cautious exposure to sunlight is essential for successful body conditioning.
Additionally, individual sensitivity to sunlight varies. To determine a person’s skin sensitivity to solar radiation, methods of biodosimetry are used. The simplest method involves using a piece of black fabric with several holes. By sequentially opening the holes, various skin areas can be exposed to sunlight for progressively longer durations. After a few hours, redness appears on the irradiated skin, which helps establish the optimal duration of sunlight exposure for an individual.
Skin exposed to ultraviolet rays becomes pigmented due to an increased accumulation of the pigment melanin. This pigmentation is a protective response of the skin, enhancing its resistance to solar radiation.
Sunbathing should begin with 10–20 minutes, gradually increasing the duration by 10–15 minutes with each subsequent session until reaching 1–5 hours (depending on individual skin sensitivity to solar radiation).
It is recommended to sunbathe after a light breakfast, lying with the feet facing the sun and occasionally changing body positions. The head should be protected from direct sunlight. After sunbathing, it is essential to rest in the shade for 10–12 minutes, followed by a shower or a swim in the sea, river, or lake.
In spring and autumn, the best time for sunbathing in the south is from 8 to 11 AM; in the central regions, it is from 9 AM to 12 PM. During the summer, especially in hot months, sunbathing should be done in the early hours.
To protect beachgoers from direct sunlight, canopies are often erected on beaches. These canopies block much of the scattered radiation, particularly the most valuable ultraviolet rays. Additionally, the canopy roof heats up and becomes a source of infrared radiation, which can adversely affect the body.
When constructing a canopy, measures should be taken to minimize the roof’s heating by the sun and to ensure that air does not stagnate underneath. Lattice and cellular roofs, as well as those designed with angles, meet these requirements. For better cooling, solid roofs can be made double-layered with an air gap between the layers to allow for airflow. The most reliable protection from the sun comes from green vegetation.
On southern beaches, in addition to intense direct solar radiation, warm air currents rise from the heated pebbles and sand, complicating the body’s heat dissipation and creating a risk of overheating. Therefore, it is better to sunbathe closer to the shore or on specially constructed platforms extending into the sea.
The effects of sea bathing on the body largely depend on water temperature, its movement, and the concentration of salts and other substances in it.
Seawater has a complex chemical composition. The salt content varies depending on geographical latitude, evaporation rates, precipitation amounts, and dilution by freshwater. The Baltic Sea contains an average of 17.7 g/L of salts, the Black Sea 17.6 g/L, the Sea of Azov 11.9 g/L, and the Caspian Sea 6.3 g/L.
The salts in seawater irritate the nerve endings in the skin of bathers, stimulating the nervous system and enhancing metabolism. Sea bathing also improves the functioning of the respiratory, digestive, and cardiovascular systems. The constant movement of water layers provides a massage effect on the body, strengthening the muscles.
The effect of bathing in rivers and lakes primarily involves skin irritation from the cool water, as freshwater, unlike seawater, cannot irritate the skin with chemical substances. However, bathing in rivers or lakes also has excellent conditioning effects on the body and promotes health.
Certain bathing rules should be followed. Unacclimatized individuals are advised to enter the water cautiously. Swimming should begin when the air temperature is no lower than 68–73°F (20–23°C) and the water temperature is at least 64–68°F (18–20°C). Healthy individuals can swim in temperatures 1–2°F lower than those specified. Morning swims are beneficial when the water is still cool, while weaker individuals should swim during midday when both the water and air are warmer.
In the first few days, swimming should be limited to 3–5 minutes, gradually increasing to 10–20 minutes in subsequent days. It is not advisable to swim on an empty stomach or to enter the water overheated and sweaty. After swimming, one should dry off thoroughly. A leisurely walk after bathing is recommended, followed by a meal and rest.
Typically, it is recommended to swim in bodies of water in the central regions in the morning (from 9 AM to 12 PM), about 1–1.5 hours after breakfast, or in the evening (from 4 PM to 6–7 PM), 2–3 hours after lunch. Healthy individuals can swim 2–3 times a day. Swimming is often combined with physical exercises and sun and air baths, with swimming serving as the concluding procedure.
Treatment with a marine climate and sea bathing, or thalassotherapy (from the Greek word “thalassa,” meaning sea, and “therapy”), is an ancient method of restoring health. In Ancient Greece, it was said, “The sea washes away all ailments.” It was believed that seawater endowed people with strength.
A beach and the entire coastal strip act as a natural inhaler, where vacationers “drink” air that is mineralized and saturated with tiny water droplets, sea salts, and phytoncides from marine algae.
When swimming in the sea, water affects the body both mechanically and through its temperature. Initially, a strong chill is felt—this is the body’s protective response aimed at reducing heat loss: blood vessels in the skin and muscles constrict. Simultaneously, blood vessels in internal organs dilate, increasing blood flow to them. This stimulates the nervous system. In response, gas exchange in the body intensifies: oxygen absorption increases, and carbon dioxide release rises, enhancing circulation. Blood vessels in the skin dilate, causing it to redden, muscles relax, and the feeling of cold is replaced by warmth. Repeating such cycles, associated with “vascular gymnastics,” during proper bathing routines with moderate sea water temperatures has significant training and conditioning benefits.
During bathing, sea salts settle on the skin as crystals, prolonging their effects on the body even after leaving the water.
The cold impact of sea bathing contributes to conditioning, enhances the burning of sugars and fats in the body, and activates kidney function. Ionized sea air has therapeutic effects on chronic inflammation of the mucous membranes of the respiratory organs. Thalassotherapy improves oxidative-reductive processes, the state of the nervous system, strengthens the functions of endocrine glands, and normalizes blood pressure and sleep.
However, it is essential to understand that the sea is a potent therapeutic factor that requires careful application. Swimming for too long, until shivering sets in, can cause irreparable harm to health.
The dosage of sea bathing depends on the state of the body, as well as the temperature of the water and air, wind strength, sunlight, cloud cover, and humidity, all of which are carefully considered by medical professionals when prescribing balneological health treatments.
Swimming in the sea is beneficial when the water temperature is above 62°F (17°C). Sea baths at temperatures of 62–64°F (17–18°C) are considered cool, 68–77°F (20–25°C) warm, and 77–81°F (25–27°C) hot.
Currently, automatic displays are being installed on the therapeutic beaches of Sochi, Yalta, and other resorts, indicating the recommended dosage of sea bathing based on weather conditions and therapeutic regimes.
On the beaches of Anapa, Evpatoria, and Gagra, indicators are often provided that characterize human thermal sensations under the simultaneous influence of temperature and humidity, wind—equivalent-effective temperature and radiation-equivalent-effective temperature, which significantly depends on solar radiation.
The most pleasant sensations and normal heat exchange with the environment occur at equivalent-effective temperatures of 63.1–71.1°F (17.3–21.7°C) when a person is undressed, and 62.1–68°F (16.7–20.0°C) when dressed.
Calculations of radiation-equivalent-effective temperature show how solar rays enhance the heating of the human body. An incoming solar energy of about 0.7 cal/cm²/min is felt as a temperature increase of 3°F, meaning that at an equivalent-effective temperature of 68°F (20°C), the radiation-equivalent-effective temperature under these conditions equals 73°F (23°C).
Methods for assessing human thermal sensations through calculations of equivalent-effective temperature and radiation-equivalent-effective temperature do not account for the influence of the large water mass of the sea, which reduces thermal load. Nevertheless, these methods are quite indicative, useful, and are currently successfully applied at resorts across the country.