Is it true that if you run a gold band across your forehead...?

and it leaves a black streak, it means you are deficient in iron? How does this work?
Answer:
OK, this is sort of true but it has nothing to do with gold. Gold is completely non-reactive as a chemical - that's why everybody likes it in jewelry, right? Because it doesn't tarnish. But if you rub yourself with a hard piece of metal it could cause a bruise. Bruises come from tiny broken blood vessels in your skin. The vessels and the blood in the vessels are dependent on the presence of iron to be healthy. If you are iron-deficient then you are more like to have bruising when you rub a ring or coin on a delicate section of skin over a bone - like your forehead.
People who are iron deficient tend to bruise more easily. It is not magical and it has nothing to do with the kind of metal you use.

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works anywhere on your skin doesn't need to just be forehead. Yes this means you are deficient in iron. Will work with a coin too

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Yes. It is true. Rub gold anywhere on your face and it will tell you if you are lacking iron in your blood. The more pure the gold is the better it will work. I do not know the technical reasoning for it though.

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I don't know how it works but it does. You don't have to run it across your forehead though any part of your face, jawline, will do.
I find that my gold rings leave black circles around my fingers when my iron is really low.

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I suppose this explains the marks people can get on their skin if they wear real gold

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