The Science of Sweat

Have you ever heard someone say, “It’s not the heat, it’s the humidity”?

What about, “Sure it’s hot, but it’s a dry heat so it’s not so bad”?

While you may not have realized it, ultimately both of those expressions have to do with a topic you may not like thinking about:  sweat.

While you may not enjoy thinking about sweat (let alone sweating), it’s actually a good thing.

Yes, I know: sweating is uncomfortable.  It can be stinky.  Sweat can mess up your hair, clothes, and makeup.  

But I’m here to tell you that sweating is a lot cooler than you might think (pun intended).

Fast Facts About Sweat

Sweat is composed of about 99% water.

The remaining 1% consists of salts (specifically calcium, magnesium, sodium, and potassium), trace minerals (including copper, zinc, and iron), waste products, and a protein with antimicrobial properties (dermcidine). 

Additional components of sweat vary based on the individual and their diet.  For example, you may have noticed that after eating meals heavy with garlic or curry, the scent of those spices may linger on your skin.  The phenomena is due to the fact that the chemicals responsible for those smells have been secreted in your sweat.

The average adult has 3 million sweat glands.

Not all sweat glands are created equal.

There are two major types of human sweat glands: apocrine and merocrine (sometimes called eccrine).  Not only is the sweat produced from each type of gland different, but the glands are found in different parts of the body and respond to different stimuli.

Diagram of the skin showing eccrine (merocrine) and apocrine sweat glands
Diagram of the skin showing eccrine (merocrine) and apocrine sweat glands

Merocrine sweat glands are the predominant sweat glands in your body and they are most abundant on the palms of your hands, the soles of your feet, and on your forehead.  These glands are activated in response to elevated body temperature and exercise. So when you “work up a good sweat”, these are the glands that are involved.

Apocrine sweat glands are less abundant in the body.  They are located primarily in the armpit and the groin, and tend to increase during puberty. These glands are activated when a person is upset, frightened, in pain, or aroused. 

In addition to all of the components listed above, sweat produced from these glands also contain fatty substances and proteins: ingredients that bacteria love to ingest.  As bacteria chow down on the sweat produced from apocrine glands, they release waste products with a distinct smell.  This is what causes the “stink” in sweat from these regions.

From here on out, I’m going to be focusing on the sweat produced from merocrine sweat glands.

The Role of Sweat in Homeostasis

Homeostasis is a fancy word that basically means the processes by which living things maintain a balance or constant level of different things in the body.  Among other things, homeostasis is involved in keeping the right balance of water and salts in our cells, in keeping our blood pressure and pH in the correct range, and keeping us at a constant body temperature.

Humans are considered warm-blooded: while slight variations in temperature can occur, our temperature generally stays around 98.6oF.  Maintaining this body temperature is important, since even slight shifts can disrupt the rates of reactions that need to occur in our bodies. And this is where sweat comes in.

If our body temperature elevates, whether because our environment is hot, we are sick with a fever, or we are physically active, there needs to be a way to cool down.

When our body temperature is elevated, we need a way to cool down. That's one reason we sweat
When our body temperature is elevated, we need a way to cool down. That’s one reason we sweat

Through some pretty amazing processes involving multiple body systems (including integumentary, endocrine, nervous, and circulatory systems), elevated body temperature triggers our sweat glands to produce sweat.  As the sweat evaporates from our skin, it takes heat with it.  This process—called evaporative cooling—lowers our body temperature.

Does it sound too simple to be true?  Trust, me: the actual process and how it takes place is anything but simple.  But it is easy to demonstrate. 

Simply wet an area of your skin with water.  You’ll notice that soon it will feel cool. That coolness you feel is actually heat leaving your body as the water evaporates. 

If you have rubbing alcohol, try the same thing again.  You’ll notice the cooling effect occurs much faster than it did with just the water.  Why? Because rubbing alcohol evaporates faster than water.

Why You Feel Hotter on a Humid Day

So back to our discussion of why humidity makes a hot day feel even hotter.

On a humid day, the air is already saturated with water.  The high level of water in the air slows down the rate of evaporation of sweat from your body.  If the sweat can’t evaporate from your skin, your body can’t cool down.  Your brain, recognizing that your body temperature is still high, responds by signalling your skin to produce even more sweat. As the feedback loop continues, you continue losing water from your body as you sweat which can lead to dehydration. This can actually be quite dangerous, so if you’re out on a hot humid day and start to feel overheated, take heed and try to cool off. 

What Happens When Our Body Gets Too Cold?

To round out our discussion of homeostasis and body temperature, you may be wondering if our bodies have a way to warm us up if we get too cold.  Yes!  That’s the reason we shiver in the cold. By shivering, the muscles in your body contract and relax and this process generates body heat to warm you.  

Wind chill or “feel like” temperatures are based on the combined effects of temperature and wind speed

This brings us to another weather-related phenomenon that effects our homeostasis: wind chill. 

On a cold day, your body heat creates a layer of insulation around you. But if the wind is blowing, it will blow away that warm layer of insulation.  Because of homeostasis, your body will counter by generating more heat, and once again the wind will blow it away. The harder the wind blows, the faster this happens. Once the wind reaches a certain speed, your body can’t keep up and is unable to generate heat fast enough to replace what is lost to the wind.  This is the basis of wind chill.    

Just as getting overheated on a hot, humid day is dangerous since you run the risk of heatstroke, so is becoming too cold on a day with wind chill advisories. If you’re not careful, you could develop frostbite or hypothermia.

I hope you come away with a better understanding of the amazing complexity of your body and the systems in place for keeping you in homeostasis. Our bodies truly are wonderful! Even when we sweat!

Related Posts

The Chemical Composition of Human Sweat

Physiology of sweat gland function: The roles of sweating and sweat composition in human health

When It Comes to Sweat, What’s Considered Normal?

Why is wind chill so dangerous?

Why is Wind Chill So Dangerous: Exploring the Science of Temperature

If you’ve got a high schooler interested in learning about homeostasis and/or the systems of the human body, I’m teaching two year-long courses starting in August, both through True North Homeschool Academy: Biology (with an optional honors track) and Anatomy and Physiology.

Both classes meet one hour a week for a live, interactive class. Then students will complete homework assignments, quizzes and tests, and hands-on labs and projects for the remainder of the week. I keep track of grading and always do my best to keep the material engaging and relevant to students. Let me know if you’d like more information about the classes or if you’d like to register.

No one likes to sweat.  It's gross.  It's stinky.  It can ruin your hair, makeup, and clothes.  But the ability to sweat is a GOOD thing.  Learn the science of what sweat is and how it is used by our body to maintain homeostasis.

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