Relatives are burdens; scratching head (5)
I believe the answer is:
aunts
'relatives' is the definition.
(aunt is a kind of relative)
'burdens scratching head' is the wordplay.
'burdens' becomes 'haunts' (haunt can mean to burden or worry).
'scratching head' means to remove the first letter.
'haunts' with its first letter taken away is 'AUNTS'.
'are' is the link.
(Other definitions for aunts that I've seen before include "Female relatives, usually older" , "Elderly female relations" , "Sally and others" , "Parents' sisters" , "relatively speaking" .)