A method of treating or preventing a hair-condition of a user comprising: subjecting the user's scalp to at least 200 distinct electrode-scalp contact events during a time-interval of at most one minute and dividable into 5 non-overlapping equal-duration sub-intervals covering the time-interval, method performed such that i. for at least a majority of the electrode-scalp contact events, no electrode of the event enters into the dermis； ii. a duration of each electrode contact event is at most 100 milliseconds； and iii. for each electrode contact event, an electrical current flows between the electrode and the scalp so as to deposit electrode-released ions of a first metal or of a second metal on the scalp, thereby forming a respective metal-ion-deposition island on the user's scalp.
