Tattoos remain visible thanks to immune cells called macrophages

The immune system fights tattoos

Our skin is a fascinating organ that wants nothing more than to protect our bodies from the outside world. Tattoos penetrate that protective wall to inject ink directly into the sensitive, immunologically rich layer of skin known as the dermis.

The body can remove tattoos after they are broken down by laser

Tattoos place blobs of ink below the surface layers of the skin in packets too large for white blood cells to clear out. By breaking the ink into smaller pieces, they can be processed by the immune system, which is responsible for removing foreign matter.

Tattoos, explained

Tattoos last because immune cells trap ink beneath the skin—but there's more to the story. This overview looks at how ancient cultures used tattoos for status, spirituality and punishment; how technology like the electric tattoo machine transformed the art form, and where innovations like smart tattoos could take it next.

A macrophage can eat 100 bacteria, on average, before it's exhausted

These specialized immune cells are first responders during inflammation, responding to a threat or injury and then performing other inflammatory response tasks, including summoning neutrophils to help attack invaders.

Tattoos are made by injecting pigments into the skin

Tattoo ink is injected under the skin, which can leave the body open to infections and allergic reactions. While many tattoo artists are licensed professionals who follow sanitary guidelines, that’s not always the case.

Harvard and MIT researchers are developing life-saving tattoos

Tattoos aren’t just a fashion statement. Scientists are trying to find life-saving applications for them. Harvard and MIT researchers are developing tattoo inks that react to body chemicals, alerting diabetics to blood sugar fluctuations or athletes to dehydration. Someday, patients may observe their body chemistry with tattoos that change colors.

Tattoo inks are largely unregulated by the FDA

With hundreds of ink manufacturers, all unregulated by the FDA, it’s hard to determine the exact ingredients in tattoo inks. Some pigments may contain carcinogenic chemicals, such as heavy metals and aromatic hydrocarbons, or even bacterial contaminants. Red ink often causes allergic reactions and may even contain lead or mercury.

Tattoos suppressed during colonization are experiencing a revival

A few decades ago, the distinct facial tattoos worn by Maori people were on the brink of disappearing. Then, Maori artists brought the cultural practice back into the spotlight. This TVNZ story follows one reporter’s mother as, at 59 years old, she receives tā moko from a Maori artist.

These cells 'taste' danger, trigger immune responses

Taste receptor-coated tuft cells are found throughout the body, where they communicate with and take part in a growing list of biological processes. In the intestines, these taste receptor-studded cells can sense byproducts of parasite metabolisms. This causes the taste receptors to release chemicals that alert the immune system, order nearby goblet cells to produce mucus, and trigger muscle contractions in attempts to launch the parasites from the intestines.

Chronic inflammation can cause cellular damage and could lead to cancer

Over time, this cellular defense system can inadvertently damage cells and tissues when it's in this heightened alarm mode over a prolonged period. This occurs because, when immune cells are sent somewhere without a true target, they may attack healthy cells and tissues.

Measles infection can cause long-term immune system “amnesia”

The measles virus attacks the body's immune system, including preying on T and B cells in the lymphatic system. These cells hold memories of past infections, which can be degraded as the virus destroys them. This leaves patients susceptible to other infections for a year or longer.

What are 'antibodies'? Read this quick overview

Antibodies are protective proteins produced by your immune system. They attach to antigens (foreign substances) and remove them from your body. Understand this important element of the immune system with this quick overview.

Adhesion molecules and intercellular junctions allow cells to connect together

While some organic structures are mostly composed of non-cellular components (e.g., collagen and calcium phosphate minerals in bones), tissues and organs composed of connected cells rely on specialized proteins and connections to create watertight seals that protect cells within the interior from environmental molecules.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

In 2015, a custom virus program was used to destroy and transform art images

At the Art Laboratory Berlin's "bOdy pandemOnium: Immersion into Noise" exhibit, Chicago-born artist Joseph Nechvatal explored viractualism—the interface between the biological and the technological—via a custom virus program that randomly altered images representing the human eye and rectum.

CRISPR-Cas systems act as genetic memory banks for defending bacterial cells

When viruses called phages inject DNA into bacteria, some bacterial species store bits of this DNA in their own genomes. This allows them to recognize and destroy the same virus if it attacks again.

Large animals like giraffes and elephants have evolved unique cancer defenses

One may expect the larger an animal is, the more likely it is to develop cancer—simply because there are more cells and more chances for a dangerous mutation. However, some large animals show cancer rates almost 10 times lower than humans—a phenomenon known as Peto's Paradox.

New blood cells are created by hematopoietic stem cells

Blood is made up of several cells with various functions and short lifespans, so the body must have a constant supply of replacements. These replacements are created by hematopoietic stem cells, rare cells that live in bone marrow and can regenerate themselves and blood cells.

Mosquito necroprinting uses an insect's mouthpart as the printer nozzle

Mosquitoes are abundant, and their nozzles are 32-100 times cheaper to harvest than to create from scratch out of metal or glass. By coating the organic nozzle to increase its strength, researchers are employing necroprinting to create tiny structures at better resolutions than commercial alternatives.

A visualization of mycoremediation, where fungi extract toxic and radioactive pollutants from soil

As organisms such as mushrooms grow, they develop large networks of root-like structures called mycelium that spread underground and release enzymes that break down contaminants. By absorbing these chemicals, fungi limit the damage caused by these toxins and localize them within the organism for easier collection and disposal.

Microtears in muscles from exercise cause fibers to grow back larger

Placing muscle under increased load or stress causes damage that requires rest to repair, leading to stronger, more enduring muscle over time. Muscles adapt to such increasing demands by improving their efficiency with approaches that include increasing the number of mitochondria housed in hundreds of thousands of muscle cells.

Ticks are extremely hard to kill

These arachnids can transmit more than a dozen diseases to humans, and they're very resilient: Some can survive extreme heat and cold, live for years without a blood meal, and even survive multiple days underwater.

Wet macular degeneration affects 10%-15% of those with macular degeneration

This form of molecular degeneration refers to when excess blood vessels form in the back of the eye and damage the macula. If someone with this condition looks at straight lines, they will typically appear wavy or crooked.

Nanoplastics can bypass the blood-brain barrier and may harm the nervous system

Nanoplastics are formed from the breakdown of microplastics and can breach cells. Their large surface area relative to size allows them to carry higher concentrations of forever chemicals than the surrounding environment into sensitive organs.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Engrams are the specific pattern of brain cells that make up a memory

Memory isn’t stored in your brain in a neat little package but is instead spread across a pattern of cells in different regions. Understanding this process could lead to better treatments for conditions like Alzheimer’s or PTSD.

Watch what the Ebola virus does inside our cells and organs in order to spread and survive.

Microchips in payment cards improve security by generating unique transaction codes

Magnetic strips store unchanging data that is easily cloned, but microchips act as miniature computers that encrypt sensitive data. They also resist fraud by creating data unique to each transaction, preventing duplication.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

The use of fungi to detoxify land and water—a process known as mycoremediation—has been used to clean up natural resources affected by the 2025 California wildfires.

The original copy of the Declaration of Independence is not a pristine document, and even features a smudged anonymous handprint in the bottom left corner.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Read a deep dive on the 'all-purpose healing' peptide BPC-157.

See these 16 pieces of art evoking phobias of snakes, flying, spiders, and more. 

The identity of the Tank Man in the iconic photo from the 1989 Tiananmen Square protests remains unknown and was possibly killed.

When you complete a CAPTCHA on a website to prove you are human, you may be unknowingly training algorithms for self-driving cars, whose systems require training data to help identify crosswalks, bicycles, and other outdoor objects.

Graffiti dates back to at least ancient Pompeii, where citizens scrawled messages to one another on public walls

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

Massive 3D printers have been used to build homes by stacking layers of 'concrete toothpaste,' a fire-resistant material that effectively insulates against outside noise.

Against his wishes, Albert Einstein's brain was removed before his cremation, and the pathologist responsible stored it for decades in mason jars within a beer cooler.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

Power lines are dotted with large, brightly colored balls to improve the visibility of these thin wires to helicopters and small planes and help prevent potential crashes.

See a 3D reconstruction of Tenochtitlan, the Aztec capital that was home to an estimated population of 200,000 to 400,000.

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.