int $user_id )
Fires before the page loads on the ‘Profile’ editing screen.
The action only fires if the current user is editing their own profile.
(int) The user ID.
Generally, action hook is used to save custom fields that have been added to the WordPress profile page.
This hook only triggers when a user is viewing their own profile page. If you want to apply your hook to ALL profile pages (including users other than the current one), then you also need to use the edit_user_profile_update hook.