The invention concerns a device (10) for treating the hair, comprising two arms (12, 4) that are able to move relative to one another between a first opened configuration for inserting hair between the arms (12, 14) and a second closed configuration for treating the hair, at least one of the arms (12, 14) comprising: —a shell, —a support housed in said shell, —a treatment plate supported by the support, —an electrical heating element received in a housing defined between the support and an inner face of the treatment plate, —a first sealing element sandwiched between the support and the treatment plate, —a second sealing element, wherein the second sealing element is sandwiched between the support and the shell.