Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

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This article has been updated for 2019.

7 Massage Guns That Are on Sale Right Now

Jawku/Actigun
Jawku/Actigun

Outdoor exercise is a big focus leading into summer, but as you begin to really tone and strengthen your muscles, you might notice some tough knots and soreness that you just can’t kick. Enter the post-workout massage gun—these bad boys are like having a deep-tissue masseuse by your side whenever you want. If you're looking to pick one up for yourself, check out these brands while they’re on sale.

1. Actigun 2.0: Percussion Massager (Black); $128 (57 percent off)

Actigun massage gun.
Actigun

Don't assume you need a professional masseur to provide relief—this massage gun offers 20 variable speeds and can adjust the output power on its own according to pressure. Can your human massage therapist do that?

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2. JAWKU Muscle Blaster V2 Cordless Percussion Massage Gun; $260 (13 percent off)

Jawku massaging gun.
Jawku

This cordless, five-speed massager uses a design that's aimed to increase blood flow, release stored lactic acid, and relieve sore muscles through various vibrations.

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3. DEEP4s: Percussive Therapy Massage Gun for Athletes; $230 (23 percent off)

Re-Athlete massage gun.
Re-Athlete

Instant relief is an option with this massage tool, featuring five different attachments made to tackle any muscle group. You can squeeze in eight hours of massage time before you have to charge it again.

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4. Handheld Massage Gun for Deep Tissue Percussion; $75 (15 percent off)

Massage gun from Stackcommerce.
Stackcommerce

With five replaceable heads and six speed settings, this massage gun can easily adapt to the location and intensity of your soreness. And since it lasts up to three hours per charge, you won't have to worry about constantly plugging it in.

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5. The Backmate Power Massager; $120 (19 percent off)

Backmate massage gun.
Backmate

Speed is the name of the game here. The Backmate Power Massager is designed for fast, effective relief through its ergonomic design. Fast doesn’t need to mean short, either. After the instant relief, you can stimulate and distract your nervous system for lasting pain relief.

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6. ZTECH Percussion Massage Gun (Red); $80 (46 percent off)

ZTech massage gun.
ZTech

This massage gun looks a lot like a power drill, and, similarly, you can adjust its design for the perfect fit with six interchangeable heads that target different muscle areas.

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7. Aduro Sport Elite Recovery Massage Gun (Maroon); $80 (60 percent off)

Aduro massage gun.
Aduro

Tackle large muscle groups, the neck, Achilles tendon, joints, and small muscle areas with this single massage gun. Four massage heads and six intensity levels allow this tool to provide a highly customizable experience.

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Do Politicians Need a Musician's Permission to Play One of Their Songs at a Campaign Event?

Dyana Wing So, Unsplash
Dyana Wing So, Unsplash

Whether it’s the songwriter, the performer, or the recording label, someone always owns the rights to a song. Whether or not one needs permission to play that song depends a lot on the circumstances. A DJ at a wedding doesn’t need to worry about any consequences for playing Peter Gabriel's “In Your Eyes” or The Righteous Brothers's “Unchained Melody.” Sports arenas can pipe in the Rolling Stones's “Start Me Up” without a release.

In the world of politics, however, campaigns and rallies that rely on music to stir up crowds often come under fire for unauthorized use. What’s the reason?

According to Rolling Stone, it’s not typically an issue over copyright, though using a song without permission is technically copyright infringement. If a song is played in a public venue like a stadium or arena that has a public performance license, no permission is needed. The license is typically granted through a songwriters’ association like the American Society of Composers, Authors, and Publishers (ASCAP) or Broadcast Music, Inc. (BMI). Even so, ASCAP still recommends [PDF] that political campaigns seek out permission from the musicians or songwriters, as these licenses exclude music played during conventions or campaign events.

Additionally, most artists aren’t concerned with their music being played at a wedding or sporting event. It is, after all, a form of free publicity and exposure, and no one is really making any substantial amount of money from their work. But the political realm is different. Because artists might have differing political beliefs than a candidate using their music, they sometimes grow concerned that use of their material might be construed as an endorsement.

That’s when artists can begin to make noise about wanting politicians to stop playing their music. In this instance, they can object on the basis of their Right of Publicity—a legal argument that covers how their image is portrayed. They can make the assertion that use of their work infringes on their right to not be associated with a subject they find objectionable. Other arguments can be raised through the Lanham Act, which covers trademark confusion (or a False Endorsement), which addresses the implication an artist is endorsing a political message if their music is used.

In 2008, for example, Jackson Browne won a lawsuit against John McCain and the national and Ohio GOP when the McCain campaign used Browne’s song “Running on Empty” in ads attacking Barack Obama over gas conservation.

Even if the musician isn’t supportive of a candidate, it’s not always advisable to take such action. A contentious legal confrontation can often result in more publicity than if a musician simply let the campaign continue uninterrupted. Other times, recording artists feel strongly enough about distancing themselves from a message they disagree with that they’ll take whatever steps are necessary.

The bottom line? More often than not, a song played during a campaign isn’t there because an artist or label gave their permission. And unless the artist strenuously objects to the campaign message and is willing to get into a legal tussle, they probably can’t do a whole lot to stop it.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.