Wearing a red thread around the thread, especially on the left hand, is a Kabbalist tradition. Kabbalah is an esoteric discipline of the Jewish mysticism. The word literally means “reception, tradition or correspondence”.
However, among the people, wearing a red thread around the wrist first became popular when Madonna started this “trend”. The people followed, without asking is there anything more deeply connected with this?
This tradition actually has nothing to do with fashion, or popularity. It is believed to protect the one who’s wearing it from something bad. An evil eye, bad intentions of people or even dark, unexplained forces…
That’s why it is believed that after a woman conceives, she should definitely wear a red thread around the left wrist, because people can be especially devious and jealous towards pregnant women. But, for the “magic” to work, the thread must be put on the wrist by the lover or one of the closest relatives.