Mark followed mother to get a cosmetic (7)
I believe the answer is:
mascara
'cosmetic' is the definition.
(I know that Mascara is a type of make-up)
'mark followed mother to get a' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'followed' says to put letters next to each other.
'mother' becomes 'ma' (ma can mean mother).
'to get' means one lot of letters go next to another.
'scar' after 'ma' is 'mascar'.
'mascar'+'a'='MASCARA'
(Other definitions for mascara that I've seen before include "Make-up item" , "Cosmetic for the eyes" , "Type of make-up" , "that accentuates lashes" , "Eyelash make-up" .)