Let’s turn a genie blue
In the magical world of Disney’s Aladdin, carpets fly, princesses have pet tigers and a pauper can become a prince with the help of a genie. The original cartoon and the new live-action film bring up a lot of questions, but one in particular stands out: Why is that genie blue?
While magical genies don’t exist, there are plenty of ways that nature can bring someone the blues.
The color people perceive as blue is a trick of the light, explains Richard Prum. He’s an ornithologist — someone who studies birds — at Yale University in New Haven, Conn. “To me, the genie is blue because the genie is substanceless,” Prum explains. “It’s the same reason the sky is blue.”
The sky is blue because of the way light scatters. Light travels in waves. We perceive different wavelengths of light as different colors. Red, for example, has long, stretched out waves. Blue’s waves are short and choppy. (This electromagnetic spectrum extends out to even longer and shorter wavelengths that we can’t see at all.)
Light from the sun consists of many wavelengths. Combined, they appear white. When that light encounters Earth’s atmosphere, it hits gas molecules. This causes the light waves to scatter in different directions. Some, such as blue, scatter more. Long wavelengths, such as red, scatter less. The result is that to us the sky looks blue.
If the genie were a gassy giant, Prum explains, the molecules in that gas would scatter short wavelengths of light and make the genie appear blue.
Bringing on the blues
But there’s more than one way to scatter light and make blue. Many real creatures flaunt blue hues in their skin. Blue-footed boobies have — you guessed it — blue feet. Other birds have blue necks or blue beaks. Mandrills — a species of monkey — have bright blue faces, while male vervet monkeys have bright blue private parts.
Prum has looked into how birds produce blue colors in their skins. He conducts this work with Rodolfo Torres, a mathematician at the University of Kansas in Lawrence. The pair carefully examined 31 bird species. All, they found, produce their blue skin the same way.
In their skin, these birds have long strands of collagen. It’s a fibrous molecule usually found in bones and tendons. Their skin’s collagen lies in a ring structure on top of a layer of melanin — a dark pigment. When light enters the skin, Prum explains, it scatters off one fiber and then a neighboring fiber and then off all the other fibers before that light finally gets reflected onto your eye. Because the collagen fibers break up the wavelengths of every color except blue, you perceive that light — and the bird’s skin — as blue.
Prum and Torres published their findings many years ago in the Journal of Experimental Biology.
The collagen in human skin isn’t arrayed in the right way to give us a Smurf-like hue. But with the right metals, people can turn blue, too. A condition called argyria can develop when someone is exposed to too much silver. “It’s not totally blue, like the genie. It’s more of a silver-blue,” says Bettina Heidecker. She’s a cardiologist, someone who treats diseases of the heart, at Charité University Clinic Berlin in Germany.
A few years ago, Heidecker treated a patient who came in with bluish skin and fingernails. He got that blue tinge in part because he had been following doctor’s orders, she says. Doctors sometimes prescribe creams containing silver for people who have wounds that fail to heal. Silver kills bacteria, she explains, so silver-containing creams can help fight infections.
But when the man’s wounds still didn’t heal, the patient started taking some pills that contained silver. He’d ordered them off the internet. “He took them every day over years,” Heidecker says. In time, the silver from the pills collected in the man’s skin. When that hue combines with the skin’s natural pinkish tint from the blood vessels inside, a person’s skin can appear blue.
Heidecker looked at a sample of the man’s skin under a microscope and saw deposits of silver everywhere she looked. And that color is permanent, she notes. “There’s no way to get it out again.” Luckily, it’s just a color and not something worse. But she cautions against ordering pills online, especially when the drugs are not approved and it’s not clear what is in them. Heidecker and her colleagues published their analysis of the patient in 2017 in the American Journal of Medicine.
If she had to make a genie blue, Heidecker say, argyria is how she’d do it. “Maybe going in and out of the bottle all the time, he got some wounds on his chest,” she says. “He might need a skin cream, and silver is very helpful.”
If you’re a genie that’s lived for thousands of years, a few hundred years of silver skin cream might just be enough to give you the blues.
antibacterial Having properties that tend to destroy or limit the growth or reproduction of bacteria.
argyria A permanent, blue discoloring of the skin due to an excessive exposure to silver-based preparations aimed at treating a medical condition.
atmosphere The envelope of gases surrounding Earth or another planet.
biology The study of living things. The scientists who study them are known as biologists.
collagen A fibrous protein found in bones, cartilage, tendons and other connective tissues.
colleague Someone who works with another; a co-worker or team member.
hue A color or shade of some color.
hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.
infection A disease that can spread from one organism to another. It’s usually caused by some type of germ.
mandrill (Mandrillus sphinx) A primate closely related to baboons. It lives in large groups called hordes in West African countries such as Cameroon, Gabon and Guinea. Its colorful face and rear send social signals to other members of its species.
melanin A family of pigments found in all types of animals. They are responsible for the dark coloring in such things as feathers, hair, fur, skin and scales.
metal Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure).
microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nitrogen A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn. It comes in two stable forms. Both have 14 protons in the nucleus. But one has 14 neutrons in that nucleus; the other has 15. For that difference, they are known, respectively, as nitrogen-14 and nitrogen-15 (or 14N and 15N).
online (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.
organism Any living thing, from elephants and plants to bacteria and other types of single-celled life.
ornithologist A scientist who studies birds, their behaviors and ecosystems.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
pigment A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
tendon A tissue in the body that connects muscle and bone.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
Journal: R.O. Prum and R. Torres. Structural colouration of avian skin: convergent evolution of coherently scattering dermal collagen arrays. Journal of Experimental Biology. Vol. 206, p. 2409. July 15, 2003. doi: 10.1242/jeb.00431.
Journal: V. Rodriguez, R.L. Romaguera and B. Heidecker. Silver-Containing Wound Cream Leading to Argyria—Always Ask About Alternative Health Products. The American Journal of Medicine. Published online January 31, 2017. doi: 10.1016/j.amjmed.2016.11.036.