Why does my sense of smell seem worse?

Nasal congestion due to colds or allergies may cause your sense of smell to decrease or disappear. This is called transient lack of smell, or anosmia. Smoking, of course, not only destroys taste buds, but also decreases the ability to smell. Overuse of nonprescription nasal sprays such as Afrin is another common cause of loss of smell. Less common causes are medical disorders such as zinc deficiency and hypothyroidism. Rarely, loss of smell can be a sign of diseases in the frontal lobe of the brain such as tumors or dementia.