Human hair colors typically range from black, brown, blonde, and red. While these hues are common, naturally occurring green hair in humans is not part of this inherent biological palette. This distinctive color often sparks curiosity.
How Human Hair Gets Its Color
Human hair color is determined by pigments called melanin, produced by specialized cells within hair follicles. There are two primary types of melanin: eumelanin and pheomelanin. Eumelanin is responsible for black and brown shades, with higher concentrations leading to darker hair. Pheomelanin, in contrast, contributes to red and yellow hues.
The specific color of an individual’s hair depends on the varying amounts and ratios of these two melanin types. For instance, black and brown hair contains mostly eumelanin, while red hair has a higher proportion of pheomelanin. Hair color can even change over time due to shifts in melanin levels.
Why Human Hair Can Appear Green
While not a natural color, human hair can indeed take on a green tint due to external factors. This phenomenon is frequently observed after swimming in pools, where copper is often the primary cause, not chlorine alone. Copper can be present in pool water from sources like pipes, algaecides, or the water supply itself. Chlorine, used as a cleaning agent, oxidizes this copper, causing it to bind to the proteins, specifically keratin, in hair strands.
This chemical reaction forms a green film that coats the hair. Lighter hair colors, such as blonde, are more susceptible to showing this discoloration because the tint is more noticeable on lighter hues. Copper can also leach into water from old or newly installed copper pipes, leading to a green tint even from tap water, especially if the water is acidic.
Green Hair Beyond Humans
The concept of natural green hair or fur is not entirely absent in the broader animal kingdom, though it manifests differently than human hair pigmentation. Sloths, for example, often appear green, but this is not due to pigments produced by their own bodies. Instead, their fur provides a habitat for symbiotic green algae that grow within the unique grooves and micro-cracks of their hair shafts.
This algal growth gives sloths a greenish coloration, offering them camouflage within their rainforest environment. The algae also provide a nutritional benefit to sloths, as they may consume it through grooming. Similarly, some polar bears can exhibit a greenish tint, which is attributed to algae growing inside their hollow hair shafts. These instances highlight biological adaptations or symbiotic relationships that result in green appearances, distinct from the pigment-based coloring of human hair.