Regardless of how warm the outside temperature may be, we always feel cool when stepping out of a swimming pool, the ocean, or a shower. Why is this so?

When you step out of a swimming pool, ocean, or shower, a key concept that comes into play is heat transfer. Heat transfer is the movement of thermal energy from one object or substance to another. In this case, when you leave the water, the heat from your body starts transferring to the water on your skin. This happens because energy naturally flows from warmer areas (your body) to cooler areas (the water on your skin). If you feel cool, it's because the process of heat transfer is taking place as energy is pulled away from your skin.

Evaporation is the process by which water molecules transition from a liquid state to a gaseous state. This is a key factor in why you feel cool after coming out of the water. For evaporation to occur, it requires energy. This energy is absorbed from the surroundings, which includes the heat from your skin.
When the water on your skin evaporates, it essentially 'borrows' the heat from your skin to change into vapor. This results in a decrease in temperature on your skin, leading to the cooling sensation you experience. The efficiency of this process can be affected by various factors such as humidity and temperature. Lower humidity levels typically result in faster evaporation and thus a more pronounced cooling effect.

The cooling effect you feel after stepping out of water is a direct result of the heat transfer and evaporation process working together. When water evaporates, it takes the heat away from your skin, which reduces the temperature. This is beneficial and has practical applications, such as in sweating, which helps regulate body temperature.
This cooling effect occurs regardless of the outside temperature. Even on a hot day, the water on your skin will still evaporate, drawing heat away and causing you to feel cool. The overall sensation of coolness can vary depending on how quickly the evaporation occurs, which in turn can be influenced by external factors like air temperature and humidity.