There’s more to sweat than “it happens.” There’s types, composition, scents, and even genetic factors that alter how you perspire.

It’s time to break out the deodorant for a seriously sweaty season. If you’ve ever wondered why we don’t just coat our entire body in the stuff, we’ve got the answers!

For how often we experience it, there’s actually a lot of interesting and sometimes weird things a lot of people don’t know about both sweat and BO — like what sweat’s composed of, how genetics affect it, or the effect of the foods we eat. So, before we kick off the sweat season of the year, here are 17 things you should know about sweat and BO.

When your body starts to sense that it’s overheating, it starts sweating as a way to control its temperature. “By promoting heat loss through evaporation, sweat helps regulate our body temperature,” explains Adele Haimovic, MD, a surgical and cosmetic dermatologist.

What your sweat is composed of depends on which gland the sweat is coming out of. There are many different types of glands on the human body, but generally, only two main ones are recognized:

  • Eccrine glands produce most of your sweat, especially the watery kind. But eccrine perspiration doesn’t taste like water, because bits of salt, protein, urea, and ammonia gets mixed into it. These glands are mostly concentrated on the palms, soles, forehead, and armpit, but cover your entire body.
  • Apocrine glands are larger. They’re mostly located on the armpits, groin, and breast area. They’re the ones most often associated with BO and produce more concentrated secretions after puberty. Since they’re near hair follicles, they typically smell the worst. This is why people often say stress sweat smells worse than other types of sweat.

So why do you smell when you sweat? You may notice the smell mostly comes from our pits (hence why we put deodorant there). This is because the apocrine glands produce the bacteria that break down our sweat into “scented” fatty acids.

“Apocrine sweat by itself does not have an odor, but when the bacteria that lives on our skin mixes with apocrine secretions, it can produce a foul-smelling odor,” Haimovic says.

Besides just cooling down, there are many reasons why our body starts producing sweat. The nervous system controls sweat related to exercise and body temperature. It triggers the eccrine glands to sweat.

Emotional sweat, which comes from the apocrine glands, is a bit different. “It does not serve a temperature regulatory function, but rather one to combat an impending challenge,” explains Adam Friedman, MD, FAAD, associate professor of dermatology at George Washington University School of Medicine and Health Sciences.

Think fight-or-flight response. If you sweat when you’re stressed, it’s because your body sends a signal to your sweat glands to start working.

“Spicy foods that contain capsaicin trick your brain into thinking that your body temperature is increasing,” Haimovic says. This in turn triggers sweat production. Spicy food isn’t the only thing you eat or drink that can make you sweat, either.

Food allergies and intolerances are often the cause of sweating while eating. Some people also experience “meat sweats.” When they eat too much meat, their metabolism spends so much energy breaking it down that their body temperature goes up.

Another thing that can increase sweating is consuming large amounts of alcohol. Haimovic explains that alcohol can speed up your heart rate and dilate blood vessels, which also occurs during physical activity. This reaction, in turn, tricks your body into thinking it needs to cool itself down by sweating.

On top of stimulating sweat, foods can also affect how you smell when you sweat. “As byproducts of certain foods are secreted, they interact with the bacteria on our skin, causing a foul-smelling odor,” Haimovic says. High levels of sulfur in foods like garlic and onions can cause this.

A diet high in cruciferous vegetables — like cabbage, broccoli, and Brussel sprouts — may also change your body odor thanks to the sulfur they contain as well.

Veggies might cause a certain smell, but a 2006 study found that a vegetarian’s body odor is more attractive than a carnivore’s. The study included 30 women who sniffed and judged two-week-old armpit pads that were worn by men. They declared that men on a nonmeat diet had a more attractive, pleasant, and less intense smell, compared to those who ate red meat.

In the past, researchers had pretty much always concluded that men sweat more than women. Take this 2010 study, for example. It concluded that women have to work harder than men to work up a sweat. However, in a more recent study from 2017, researchers found that it actually has nothing to do with sex, but instead has to do with body size.

It’s pretty common knowledge that BO causes more of a stink after puberty. But as hormone levels fluctuate, it can change again. Researchers looked into body odor and aging and detected an unpleasant grassy and greasy odor that was only in people 40 and over.

People often use deodorant as an overarching term when it comes to BO-masking sticks and sprays. However, there’s a key difference between deodorant and antiperspirants. Deodorants simply mask the smell of body odor, while antiperspirants actually block glands from sweating, typically using aluminum to do so.

Do antiperspirants cause cancer?There’s been a lot of discussion about whether the aluminum in antiperspirants causes breast cancer. Although scientists have hypothesized a connection, the American Cancer Society says there’s not enough scientific evidence to support this claim.

Just as it is odorless, sweat itself is also colorless. With that being said, you might notice that some people experience yellow stains under the arms of white shirts or on white sheets. This is due to a chemical reaction between your sweat and your antiperspirant or clothes. “Aluminum, an active ingredient in many antiperspirants, mixes with the salt in sweat and leads to yellow stains,” Haimovic says.

This gene is known as ABCC11. A 2013 study found only 2 percent of British women surveyed carry it. Funny enough, of the people who don’t produce body odor, 78 percent said they still use deodorant almost every day.

ABCC11 is more prevalent in East Asian people, while Black and white people don’t have this gene.

Some people are saltier sweaters than others. You can tell if you’re a salty sweater if your eyes sting when sweat drips into it, an open cut burns when you sweat, you feel gritty after a sweaty workout, or you even just taste it. This may be tied to your diet and because you drink a lot of water.

Replenish lost sodium after an intense workout with sports drinks, tomato juice, or pickles.

The amount you sweat is dependent on genetics, both on average and to the extreme. For example, hyperhidrosis is a medical condition that causes someone to sweat more than the average person. “People with hyperhidrosis sweat approximately four times more than what is needed for cooling the body,” Friedman explains. Nearly 5 percent of Americans have this condition, notes a 2016 review. Some cases are due to genetics.

On the totally opposite end of the spectrum, people with hypohidrosis sweat too little. While genetics factor into this, medication to treat nerve damage and dehydration can also be credited as a cause.

The last of a genetic sweating disorder is trimethylaminuria. This is when your sweat smells like fish or rotting eggs.

A heteronormative 2009 study looked at whether or not smell was identical from both pits. Researchers’ theory was that “increased use of one arm” would change the odor samples. They tested this by having 49 females sniff 24-hour-old cotton pads. The survey rated no different in right-handers. But in left-handers, the left-side odor was considered more masculine and intense.

According to 2015 research, you can produce a certain odor that indicates happiness. This scent is then detectable by others, stimulating a feeling of happiness in them as well.

“This suggests that somebody who is happy will infuse others in their vicinity with happiness,” said the lead researcher, Gün Semin, in a press release. “In a way, happiness sweat is somewhat like smiling — it is infectious.”

Emily Rekstis is a New York City-based beauty and lifestyle writer who writes for many publications, including Greatist, Racked, and Self. If she’s not writing at her computer, you can probably find her watching a mob movie, eating a burger, or reading a NYC history book. See more of her work on her website, or follow her on Twitter.