Merciful anosmia is seen in:
Atrophic rhinitis
Allergic rhinitis
Ethmoidal polyposis
Wegener's granulomatosis
In atrophic rhinitis, there is foul smell from the nose, making the patient a social outcast though the patient himself is unaware of the smell due to marked anosmia which accompanies the degenerative changes. This is called as merciful anosmia.