Hi..
Welcome to HEALTHCARE MAGIC..
As per your query the most common cause for foul smell from nose is
sinus infection causing
Sinusitis and inflammation of sinus caused by infection leads to a foul smell from nose..
Other causes can be nasal polyp, upper respiratory infections etc but sinusitis is the most common and probable cause..
I would suggest you to consult an Otolaryngologist and get evaluated and if sinus infection is suspected he can advise you to get a PNS view
x ray as well as MRI SCAN of the sinus done to rule out for any infection or polyp formation in the sinus or nose..
For sinus infection antibiotics like
Clindamycin can be advised, anti-inflammatory painkillers, saline irrigations,
steroid sprays and steam inhalations can relieve..
Polyps in nasal lining or sinus can be removed surgically..
Hope this information helps..
Thanks and regards..
Dr.Honey Nandwani Arora.