It is based on human observation and experience. Islam only addresses issues which have some ethical flaw in them, otherwise all fields of study have been left open for humans to study and explore. As far as Palmistry is concerned, it is again not an established science, but rather based on some repetition of events for which some causuality has been determined with the lines of the palms. There’s nothing wrong with approaching this subject however, one should be cautious of not getting astray and falling into any polytheistic notion or other unethical activities. Such activities also involve baseless speculations and we Muslims have been ordered not to follow speculations as it is a major sin. Since not being an established science, these sciences have more room to deviate a person into otherwise prohibited realms.

https://youtu.be/eCao-sI-6DY