Mago no Te (Back-Scratcher)

"Mago no te" literally means a grandchild's hand, and is a rod-shaped tool that is used for scratching one's back.

Since itches on back have been a common stress for people throughout the world, similar tools have used all over the world.

Therefore, it's not known when and who invented it.

In Japan, mago no te is normally made of wood or bamboo; the tip is bent and it looks like a cupped hand.

Actually, I thought that since it looked like a grandchild's hand, it was called mago no te, but I was wrong.

The etymology comes from a mythical fairy of China, whose name is Mako.

Mako had a very long nails, and it was thought that it would feel good if she scratched itchy spots.

This "Mako no te" (Mako's hand) was introduced to Japan, and the name became "mago no te" (grandchild's hand).

孫の手

孫の手は、背中などの手が届かない部位を掻くために使う、棒状の道具です。

背中がかゆいのを解消したいというのは人類共通の悩みであることから、同じような道具が世界中で用いられています。

このため、いつ誰が発明したかなどは、よくわかっていません。

日本では木または竹が用いられることが多く、棒の先端が曲げられ、手を丸めたような形をしています。

私は、「孫の手」のような形だから「孫の手」と呼ぶものだと思っていましたが、これは誤りでした。

語源は中国の伝説上の仙女、麻姑から来ています。

麻姑は爪を長く伸ばしており、その長い爪でかゆいところを掻くと気持ちが良さそうと考えられていました。

この「麻姑の手」が日本に伝わり、「孫の手」へと変化したそうです。

• "Mago no te" literally means a grandchild's hand, and is a rod-shaped tool that is used for scratching one's back.
• "Mago no te" literally means a grandchild's hand, and is a rod-shaped tool that is used for scratching one's back.

• Since itches on back have been a common stress for people throughout the world, similar tools have used all over the world.
• Since back itches on back have been a common source of stress for people throughout the world, similar tools have been used all over the world.

  This is correct, but using "the world" twice looks bad in formal written English. Try to change the last clause (the part of the sentence separated by the comma) to something else that means the same.
  
  For example, instead of "used all over the world" you can say "across the globe" or "across the Earth". These all have the same meaning without repeating words.

• Therefore, it's not known when and who invented it.
• Therefore, it i's not known when orand who invented it.

  This is also correct and you can say this sentence this way. The correction is another way of saying it which is more formal.
  
  Use "or" instead of "and" in this context.

• In Japan, mago no te is normally made of wood or bamboo; the tip is bent and it looks like a cupped hand.
• In Japan, mago no te is normally made of wood or bamboo; the tip is bent and it looks like a cupped hand.

• Actually, I thought that since it looked like a grandchild's hand, it was called mago no te, but I was wrong.
• Actually, I thought that since it looked like a grandchild's hand, it was called mago no te, but I was wrong.

  The "actually" is not needed in this sentence, but you can still say it.

• The etymology comes from a mythical fairy of China, whose name is Mako.
• The etymology comes from a mythical fairy of China, whose named is Mako.

  This is correct, the correction is another way of saying it.

• Mako had a very long nails, and it was thought that it would feel good if she scratched itchy spots.
• Mako had a very long nails, and it was thought that it would feel good if she scratched itchy spots.

This is very well written to a high level of written English, with some minor mistakes with grammar.