In a series of ‘Stump The Rabbi’ questions, Rabbi Yossi Paltiel, a popular Crown Heights teacher and mentor, answers many interesting questions. In this clip he responds to: “Red strings, the evil eye, and the Chabad approach?” • Watch
A Bocher once asked the Rebbe about it, The Rebbe answered him that it’s close to Avoda Zara.
In the name of Rabbi Leibel Schapiro of Miami. (who adds that he found a makor for it)
One of the items necessary for the building of the Holy Sanctuary was red thread. The dye for the red thread came from a type of worm. Rabbi S. R. Hirsch points out that the worm was the lowliest form of life, and yet it was intrinsic to the building of the Sanctuary.
The red string is thought by some to ward off the “evil eye.” Rabbi Eliyahu Dessler explains the “evil eye” as follows: If a person is blessed with good fortune and he becomes haughty as a result, this might arouse jealousy in others. In this sense, his good fortune is negative. This calls his good fortune into question and may cause him to be re-judged in Heaven.
The red thread, reminiscent of the lowly worm, can be seen as protection against this. Each time a person looks at the string he is reminded that a person is really as lowly as a worm. This humility is the ultimate weapon against the “evil eye.”
Having said that, many great Rabbis frown upon it.
What does it mean when it falls off the wrist? It is an extremely significant sign: It signifies that it was not tied on properly.
Michtav M’Eliyahu V.4 pp. 5-6