Then special glands in your skin called — what else? Sweat is also known as perspiration say: pur-spuh-RAY-shun , and it is made almost completely of water, with tiny amounts of other chemicals like ammonia say: uh-MOWN-yuh , urea say: yoo-REE-uh , salts, and sugar. Ammonia and urea are left over when your body breaks down protein. The sweat leaves your skin through tiny holes called pores.
When the sweat hits the air, the air makes it evaporate this means it turns from a liquid to a vapor. As the sweat evaporates off your skin, you cool down. Sweat is a great cooling system, but if you're sweating a lot on a hot day or after playing hard you could be losing too much water through your skin.
Then you need to put liquid back in your body by drinking plenty of water so you won't get dehydrated say: dee-HI-drayt-ed. Sweat isn't just wet — it can be kind of stinky, too. In this activity you can observe this cooling power in action—ready to get cool? Background The process of changing a liquid into its gaseous state is called evaporation. Every liquid can be turned into a gas if enough energy is added to the liquid in the form of heat.
The energy needed for the transformation is known as the heat of evaporation. How much energy you need depends on factors such as the type of liquid or the surrounding temperature. If it is already very hot outside, you will need less energy to vaporize a liquid; if it is very cold, you will need more. In order to turn into a gas the molecules held together inside the liquid have to break free to get into the air.
This means the hydrogen bonds holding the molecules together need to be broken. Thus, molecules that are able to form lots of hydrogen bonds among themselves are much harder to turn into a gas and have a higher heat of evaporation.
This also affects the boiling temperature of a liquid. Molecules that attract one another very strongly start to boil at higher temperatures compared with those that have weak attractions.
A lower boiling point generally means a liquid will evaporate more quickly. Water, for example, with one oxygen and two hydrogen atoms, can form two hydrogen bonds per molecule. Its heat of evaporation is 2, joules per gram, or calories per gram, and it starts boiling at degrees Celsius degrees Fahrenheit. Your body makes use of the evaporative process when sweating.
Sweat, which consists of 90 percent water, starts to evaporate. The necessary heat of evaporation is extracted from the sweat itself, which leads to a heat transfer from the liquid into the gaseous state. This results in a cooling effect called evaporative cooling that helps to maintain body temperature and cools the body down when it gets too hot. The degree of cooling is dependent on the evaporation rate and heat of evaporation.
In this activity you will find out which liquid has a greater cooling power: rubbing alcohol or water. What do you think will cool more when it evaporates? Observations and results Did you feel the cooling power of water and rubbing alcohol? Both liquids should feel cold on your skin. Blowing on your wet hand helps the water and alcohol to evaporate. The airflow will also support the heat transfer away from your skin.
You should have noticed that your skin feels much cooler when you put the rubbing alcohol on your hand compared with the water. The water and the alcohol will start to evaporate once you start blowing on your hand. Compared with water, alcohol has a lower heat of evaporation.
That means that for the same amount of liquid, more heat transfer occurs during the evaporation of water compared with the alcohol. Some known causes include:. In most cases, no investigations are required to diagnose hyperhidrosis. Occasionally, a blood test for thyroid disease is recommended. Reduced sweating is called hypohidrosis if there is partial loss of sweating, or anhidrosis if there is complete lack of sweating. This can occur for a number of reasons, which include:.
Lack of sweating may create problems of temperature control and lead to steep rises in body temperature during hot weather. Occasionally, this can be life threatening.
Heat stroke or sun stroke can occur in hot weather when not enough sweat is produced to keep the body cool. Symptoms can include:. Excessive loss of body salts and water can lead to a life-threatening complication known as heat exhaustion. Heat stroke can be managed, and heat exhaustion prevented, by seeking a cool, shaded place, drinking plenty of fluids and sponging the body with water, if necessary.
This page has been produced in consultation with and approved by:. Bedbugs have highly developed mouth parts that can pierce skin. In most cases, we do not know what causes birthmarks. Most are harmless, happen by chance and are not caused by anything the mother did wrong in pregnancy. If you are bitten or stung by an insect or animal, apply first aid and seek medical treatment as soon as possible.
A blister is one of the body's responses to injury or friction. Severe blushing can make it difficult for the person to feel comfortable in social or professional situations. Content on this website is provided for information purposes only.
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