A medical condition that results in exotic hair color and have reasonable side effects?

Question

So I'm designing that world with several species that all go back to a single empire that after it's fall had things radically change for the whole world.

One of the things we all know and love about fiction is the crazy hair colors. While magic exists I'm loath to introduce it in this point and simply want the following.

An actual plausible, as in breaks no scientific laws but may not exist, medical condition that results in the humans of that race having their hair follow all our laws except it has crazy color like blue or green and has a sort of side effect.

The race are 100% humans but long ago they dwelled in a small country, think a small kingdom.

Now I'd love the side effect to be tied in with the color thing because I can just make it up and said: Because of the element hioglatrin in their food that resulted in their hair taking more exotic color but has the side effect of random pain attacks in their adults.

Just an example.

Anyway It there is a hard scientific limit to what the side effect is then great. If not then what is the most realistic side effect? If it does not matter then it is fine.

I know it sounds stupid but I know very little of biology and this is theoretical biology so that' pretty tough for me.

This hair condition and side effect, if any, can be the result of anything but here is a few ideas to make to more fitting to the world.

• A particular food in their original habitat.
• Exposure to magical powers that resulted in that condition overtime.
• An element in the water.
• An element in the air.
• A sort of disease that they developed immunity to after a while but not without side effect.

Honestly whatever you want. I just want a scientific solution.

Answer 1

Follicle Fungus (and flamingos):

Hair is protein, and any protein is a snack for an organism. There are many diseases that can affect the hair, and if the goal is to have weird hair, fungus-stained works. a lot of these diseases cause hair loss as the fungus makes the hair so brittle it falls out/breaks off near the skin. If the fungus created a hyphae through the length of the hair strand, it would potentially provide enough structural support on it's own to keep the hair intact. Or, if you WANT the side effect to be brittle hair, make it brittle hair and bald spots.

If the fungus (or insert alien organism here) is of a particular color, then the resulting hair will be the color of the fungus, or stained the color of the fungus. If the fungus has different strains, then each strain could have a particular color. Maybe this even has a useful function for the fungus - the people with lime green hair tend to hang out together, and thus the hair fungus has brought potential sporulation partners into proximity.

• The Easiest side effect, as I mentioned, is bald spots and brittle hair. Most people don't like this, and would treat it, so this may not be the most desirable option.
• Some fungi produce psychoactive compounds, so imagine a side-effect where people chew on their own or other's hair to get high, or hallucinate. You could even sell your hair to people for money. They might absorb some of this through their scalp. Certain ports might require people so affected to shave before entering (to limit drug supplies) or even undergo anti-fungal treatments, permanently altering appearance.
• Chemical signals from the fungus could trigger the growth of fruiting bodies under specific conditions (like a certain number of blaze orange-haired people in close proximity). Everyone goes suddenly bald as their hair turns to spores, and unaffected people in the area are infected with the transforming hair fungus. (combine this with the drug effect, and people might WANT to be affected, so interesting story elements).
• Maybe a friendly hair fungus releases hormones that stimulate hair follicles to grow rapidly. Bald people regrow hair, which gets to be longer faster. It thus creates more food supply...

Another alternative is the flamingo effect. Flamingos are naturally white, but a microorganism in their food produces a dye that absorbs into the flamingo feathers. The result is pink flamingos. A person from a world where everyone started blonde and a blue dye has made everyone's hair turn green might seek their native foods to maintain a cultural identity. Aging with this would mean as people's hair "whitened" it might go from green to blue-ish. Pick your color and effect!

• A side effect here is that very colored compounds are likely to also show up in the skin, so green har may also mean greenish skin. People visiting a world might be described as being colorless or (whatever opposite color you choose) while those who had lived there a long time might be complimented as "getting a healthy color."

One more possibility is to have something exposing the person to large amounts of copper, which can turn hair green. Other metals can have their own effects and colors, but if the metals were too toxic, you may need some handwavium to make this work. You could even combine a fungus or bacteria with this, so the fungus on someone's scalp is actually chelating dangerous metals or compounds out to the person and depositing these in the person's hair. Thus the person could actually getting a tangible benefit from their "infection." If these compounds include toxins like tobacco or other alkaloids like ergot toxins, then the hair could once again be used like a drug.

Check out these fungi for inspiration. There are even bioluminescent ones.

Answer 2

There is no natural way to create permanent exotic colors in human hair¹

Assumption: I've added this assumption based on one of @John's comments to my answer. I'm assuming that by "exotic" what you mean is "a color other than what can naturally occur to a human in real life." In other words, white hair (regardless how you get to it) isn't exotic. Examples of exotic colors include blue, green, and my personal favorite, magenta. And there's no permanent way to get to them in real life (argyria doesn't affect hair color other than to give it a metallic look).

The proof is simple — if it were possible it would have been marketed eons ago. The reality is that there are only temporary solutions — and if a temporary solution is good enough for you then you might as well use hair dyes.

But may I submit my answer to "How would a humanoid naturally grow green hair?" for consideration?

It discusses the fact that human hair color is controlled by two pigments: eumelanin and pheomelanin.

The more eumelanin you have, the darker brown-to-black you get. The more pheomelanin you have, the more orange-to-red you get. Add the two together and you get auburn. So, based on "reality," there is no way to get green hair from brown, orange, and red.

But what if we could introduce a third pigment? Suddenly you have the ability to shift hair color to pretty much anything you want. And since you have magic in your world, a natural consequence of using magic (or, perhaps, specific types of magic or magic for specific purposes) is the introduction of this third pigment.

What you have is a (*ahem*) scientifically explicable reason for the change in hair color that rationalizes why your magic leads to it.

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_{¹ This is an important statement. Hair grows. To permanently change the color of human hair through a biologic or poisoning context would mean the agent changing the color of the hair continues for the rest of the person's life. That means the taint continues to be fed into the hair regardless of a cure or resolution to the poison. The truth is, once the intake of poison has stopped (such as the accumulation of silver salts leading to argyria) or the medical condition has been cured, there's no longer anything new to feed into the hair. It grows out, returning to its natural age-based color. This is fundamentally the reason for my answer. A permanent change to a color that cannot be accounted for by the two pigments in human hair quite literally means either changing the nature of the pigments or adding new pigments. Now, to be fair, if the disease is incurable or the poison unavoidable, then you have a "permanent" change. I'm presenting an alternative that doesn't require explaining why an illness can't be cured or a poison avoided.}

_{However, it's important to point out that if you do opt to go with illness or poison, there is a natural limitation you would either need to explain or ignore—the other pigments are still there. If you have naturally brown hair and something adds blue to it, it doesn't turn blue, it turns a dark muddy bluish brown. Thus, whether you accept my answer or another, part of the problem is that you must explain why (e.g.) the eumalenin was either subdued or replaced by the tainting agent to get a pure blue hair.}