Skin Really Is Your Biggest Organ

It can be tempting to think of skin as the scientific equivalent of the frosting on your body’s cake, but it’s an organ as complex and important as the heart or liver. It’s also really heavy: The scientific consensus is that the entire, three-layer organ makes up about 16% of a human’s weight — equal to about 20 pounds for a 125-pound person. That’s the equivalent of four bricks or a miniature schnauzer. If you consider only the external surface of the skin, that weighs about 6% of the weight of any given person.

Your next-heaviest organs — the liver (3 pounds), brain (3 pounds), and lungs (2.2 pounds) — don’t even compare. Thanks to its vast surface area and triple-layered composition, your skin efficiently keeps your other organs from getting out and other stuff from getting in, all while flexing, stretching, and renewing itself continuously.

Skin Is a Habitat All Its Own

You may have heard of the gut microbiome, but did you know your skin has its own microbiome, too? Your skin plays host to millions of microorganisms — tiny microbial communities that hitch a ride on, and even help, the exterior of your body.

The types of microorganisms that live on your skin vary depending on what type of terrain they encounter: moist or oily, exposed or enfolded, hairy or bare. They fall into four categories: viruses, bacteria, fungi, and mites. And they don’t just live there rent-free: Some of the critters crawling on your skin right now are thought to perhaps even play a part in teaching your T cells how to respond to harmful invaders. Others, like the common S. epidermidis, actually help your body defend itself against water loss and other damage.

Your skin colonies also change as you age. In fact, baby skin is thought to be sterile until the moment it encounters the world outside the womb. That’s when an important time for skin microbiome growth begins — a developmental heyday for your skin’s immune system. As a result, the skin microbiomes of babies and adults are thought to vary significantly, though research on both is still in its infancy.

Your Diet Can Influence Your Skin’s Color

Folktales about carrots improving your night vision are mere propaganda. But there’s truth to the old line that you “are what you eat” — and it can be found on your skin’s surface, which can actually change color when you consume lots of the pigments found in red, yellow, and orange veggies like carrots. Known as carotenoids, these pigments impart what scientists call an “attractive yellow-orange color to skin.”

Sound like a ploy by Big Carrot? It isn’t. Carotenoid pigments can build up in the skin, producing a yellowish hue that is associated with a healthier body. That’s where the attraction part comes in: In a variety of studies, researchers have shown that people prefer the appearance of people who eat lots of carotenoids, likely because they signal a person has a healthy diet and higher perceived health. Both indicate the person is a desirable mate — all the more reason to grab a carrot and chow down.

If We’re Going to Mars, We’re Going to Need Better Skin Care

Astronauts returning to Earth don’t just have to readjust to gravity: Many contend with skin issues. In fact, researchers note that skin problems are the most common health conditions experienced by astronauts, far outpacing skin ailments on Earth. Astronauts’ skin has endured everything from irritation due to on-board equipment to dryness and infections on space flights and at the International Space Station. Research has even shown that the complex skin microbiome undergoes changes while in space.

Microgravity, radiation, and the harsh environment of spacecraft seem to be the culprit, but scientists are still learning more about how space travel affects skin. With long-term space missions to Mars and elsewhere on the horizon, finding out how space affects skin has become a priority for researchers and private industry alike. As a result, a Colgate-Palmolive skin care company staged the first-ever in-space skin care experiment in 2022, and in 2023 another private sector experiment on the International Space Station is expected to test how lab-grown skin tissue grows in space. Insights from those studies and future inquiries could lead to the development of new skin protectants or inform skin care products down here on Earth, helping the planet-bound protect themselves against the ordinary ravages of aging.

Tattoos Are Permanent Thanks to Dead Immune Cells

If your mom warned you that your ink is forever when you announced your intention to get a tattoo, she was right. But not for the reason you might think. While common wisdom has it that tattoo ink bypasses the permeable top layers of the skin and remains embedded in the dermis, the second skin layer, the truth is a bit more complicated — and more interesting. Recent research has revealed that macrophages, a type of white blood cell that specializes in gobbling up invasive pathogens, mistake tattoo ink for an infectious cell and flock to the scene to protect the body from the foreign substance. They show up, encircle the ink, and process it.

If macrophages clean up the ink, and the immune cells aren’t immortal, then why do tattoo markings last so long? Scientists asked the same question, and mouse studies led to an eerie answer: Once the macrophages die off, even more macrophages are thought to swoop in, eating the ink their dead brethren once contained. This generational turnover means tattoo ink can last for years with minimal fading — and keep Mom’s name intact for a lifetime.

The Bible Contains Ancient Skin-Care Advice

The Bible may be a religious text, but it’s also packed with information and stories about skin care. Researchers consider the Book of Job’s description of the long-suffering Job’s chronic skin boils an accurate and early depiction of an actual genetic disease called AD-HIES (loss-of-function, autosomal dominant hyper-IgE syndrome). Nicknamed Job syndrome, the genetic disorder causes, you guessed it, boils all over the body.

A slightly lovelier tale can be found in the Old Testament story of Esther, which refers to a 12-month-long beauty and purification ritual undergone by would-be concubines of King Ahasuerus of Persia. Along with her fellow applicants to the king’s harem, Esther spends six months applying oil of myrrh to her body, and another six months putting on perfumes and other cosmetics. Only after the women have spent months doing the biblical equivalent of a makeover are they qualified for the king’s romantic consideration.

But what is myrrh, and why was it part of the elaborate beauty ritual? The name comes from Commiphora myrrha, a spiny, squat tree with fragrant sap that was used in religious rituals, to perfume cosmetic oils, and even as medicine to treat achy muscles and wounds. It wasn’t just placebo: The prized resin is stuffed full of substances that have anti-inflammatory and antimicrobial properties, which may also have improved the look of the skin.