Spending a day at the beach may leave you feeling exhausted - but there are three reasons why:

  1. Protection from UV rays - the sun gives off ultraviolet radiation which can damage cells. To repair the damage, your body mounts an immune response which increases blood flow to your skin and decreases core body temperature.
  2. Thermoregulation - your body needs to stay at 37 degrees Celsius in order to function properly, and sweating helps to maintain this temperature. This increases your metabolic rate and causes you to lose water.
  3. Dehydration - when water levels are low, blood is harder to circulate and your heart has to work harder and beat faster to bring oxygen to your organs, which makes you tired.

To avoid exhaustion, remember to wear sun protection, cool off, and drink plenty of water.