Sunbathing has been used to strengthen the body since ancient times — a practice now called heliotherapy. In Ancient Greece and Rome, sunbathing was a regular part of daily wellness: baths and even rooftops featured special rooms or sun terraces for that purpose. During the Middle Ages, medicinal use of sunlight was limited, but the physician Avicenna wrote that sunlight could protect against disease. Today, scientists have studied the effects of solar radiation on the human body and linked those effects to the light’s spectral composition. The body’s reaction to infrared (wavelengths of 760–2300 nanometers), visible (400–760 nanometers), and ultraviolet (295–400 nanometers) rays varies significantly.
Exposure to infrared sunlight raises tissue temperature. The biological effects of ultraviolet rays include bactericidal action, the formation of calciferol (vitamin D), and characteristic skin reactions such as redness and increased pigmentation. The impact of ultraviolet radiation depends on the wavelength of the rays.
Used correctly, sunlight can help strengthen the body; used improperly, it can be harmful, causing sunburn or heatstroke. That makes it important to understand how sunlight affects the body depending on exposure time, the season, and local conditions.
Any part of the solar spectrum (infrared, visible, and ultraviolet) can cause skin burns, but sunburns most commonly result from excessive absorption of the shortest rays — ultraviolet radiation.
In the mildest sunburn, the skin reddens because capillaries remain dilated for a long time. In more severe cases, the upper layers of the skin peel away and blisters form; the blisters can later burst. Excessive ultraviolet exposure can cause necrosis of skin areas. If a burn covers large portions of the body, it can raise body temperature and cause nausea.
With intense, prolonged exposure to solar radiation, especially without protecting the head from direct sunlight, heatstroke can occur. Heatstroke requires immediate medical attention.
When you sunbathe, 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, the more it scatters — for example, ultraviolet rays scatter more than visible rays. Scattered light can reach significant intensity, which is why gradual, cautious exposure to sunlight is essential when conditioning the body.
Individual sensitivity to sunlight varies. To determine a person’s skin sensitivity, practitioners use methods of biodosimetry. The simplest method uses a piece of black fabric with several holes. By opening the holes one by one, different skin areas are exposed to sunlight for progressively longer durations. After a few hours, redness appears on the irradiated skin, which helps establish the optimal sunlight exposure time for that person.
Skin exposed to ultraviolet rays becomes pigmented because melanin accumulates. That pigmentation is a protective response, increasing the skin’s resistance to solar radiation.
Begin sunbathing with 10–20 minutes, and increase each session by 10–15 minutes until you reach 1–5 hours, depending on your skin’s sensitivity to solar radiation.
Sunbathe after a light breakfast. Lie with your feet toward the sun and change position occasionally. Protect your head from direct sunlight. After sunbathing, rest in the shade for 10–12 minutes, then take a shower or go for a swim in the sea, river, or lake.
In spring and autumn, the best time to sunbathe in southern regions is 8–11 AM; in central regions, 9 AM–12 PM. In summer, especially during hot months, limit sunbathing to the early hours.
Beaches often have canopies to protect visitors from direct sunlight. Canopies block much of the scattered radiation, particularly the most biologically active ultraviolet rays. But canopy roofs heat up and become sources of infrared radiation, which can affect the body.
When building a canopy, minimize roof heating and prevent air from stagnating underneath. Lattice and cellular roofs and roofs designed with angles meet these requirements. For better cooling, make solid roofs double-layered with an air gap between the layers to allow airflow. The most reliable protection from the sun is provided by green vegetation.
On southern beaches, warm air currents rise from heated pebbles and sand, making it harder for the body to dissipate heat and increasing the risk of overheating. For that reason, sunbathe closer to the shore or on specially constructed platforms that extend into the sea.
The effects of sea bathing on the body depend largely on water temperature, water movement, and the concentration of salts and other dissolved substances.
Seawater has a complex chemical composition. Salt content varies with latitude, evaporation rates, precipitation, and dilution by freshwater. The Baltic Sea averages about 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 stimulate nerve endings in the skin, activating the nervous system and boosting metabolism. Sea bathing also improves the functioning of the respiratory, digestive, and cardiovascular systems. The constant movement of water layers provides a massage effect, which strengthens muscles.
Bathing in rivers and lakes mainly stimulates the skin through cool water; freshwater does not have the same chemical stimulants as seawater. Still, river and lake bathing have strong conditioning effects and promote general health.
Follow basic bathing rules. Enter the water cautiously if you are unacclimatized. Begin swimming when the air temperature is at least 68–73°F (20–23°C) and the water temperature is at least 64–68°F (18–20°C). Healthy people can swim in water 1–2°F cooler than those values. Morning swims are good when the water is still cool; people less tolerant of cold should swim at midday when both water and air are warmer.
Limit swimming in the first days to 3–5 minutes, then gradually increase to 10–20 minutes. Avoid swimming on an empty stomach or entering the water overheated and sweaty. Dry off thoroughly after swimming. Take a leisurely walk after bathing, then eat and rest.
Typically, swim in central-region waters in the morning (9 AM–12 PM), about 1–1.5 hours after breakfast, or in the evening (4–6/7 PM), 2–3 hours after lunch. Healthy people 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 — thalassotherapy (from the Greek thalassa, meaning sea, and therapy) — is an ancient health-restoration method. In Ancient Greece it was said, “The sea washes away all ailments.” People believed seawater gave strength.
A beach and the coastal strip act as a natural inhaler: vacationers breathe air mineralized and saturated with tiny water droplets, sea salts, and phytoncides from marine algae.
When you enter the sea, water affects the body mechanically and through temperature. At first you may feel a strong chill — a protective response that reduces heat loss: blood vessels in the skin and muscles constrict while vessels in internal organs dilate, increasing blood flow to them. That stimulates the nervous system and intensifies gas exchange: oxygen uptake increases and carbon dioxide release rises, improving circulation. Later, skin vessels dilate, the skin reddens, muscles relax, and the cold feeling gives way to warmth. Repeating these cycles during properly dosed bathing in moderately cool seawater provides significant training and conditioning benefits — a kind of “vascular gymnastics.”
During bathing, sea salts settle on the skin as crystals, prolonging their effects even after you leave the water.
The cold impact of sea bathing contributes to conditioning, increases the burning of sugars and fats, and activates kidney function. Ionized sea air benefits chronic inflammation of the respiratory mucous membranes. Thalassotherapy improves redox processes, benefits the nervous system, supports endocrine function, and helps normalize blood pressure and sleep.
However, the sea is a powerful therapeutic factor that must be used carefully. Swimming until you start shivering can cause serious harm.
The dosage of sea bathing depends on the body’s condition and on water and air temperature, wind strength, sunlight, cloud cover, and humidity — factors medical professionals consider when prescribing balneological treatments.
Swimming in the sea is beneficial when the water temperature is above 62°F (17°C). Sea baths at 62–64°F (17–18°C) are considered cool, 68–77°F (20–25°C) warm, and 77–81°F (25–27°C) hot.
Automatic displays are being installed on therapeutic beaches in Sochi, Yalta, and other resorts to indicate recommended sea-bathing dosages based on weather conditions and therapeutic regimens.
On the beaches of Anapa, Evpatoria, and Gagra, indicators often report measures that characterize human thermal sensations under the combined influence of temperature, humidity, and wind — equivalent-effective temperature and radiation-equivalent-effective temperature, the latter of which depends strongly on solar radiation.
The most pleasant sensations and normal heat exchange 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 increase 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, so at an equivalent-effective temperature of 68°F (20°C), the radiation-equivalent-effective temperature under those conditions equals 73°F (23°C).
Methods that assess human thermal sensations by calculating equivalent-effective and radiation-equivalent-effective temperatures do not account for the cooling influence of the sea’s large water mass. Nevertheless, these methods are indicative, useful, and are successfully applied at resorts across the country.
