You'd never get anything done if you couldn't ignore most of the sights, sounds, smells, and touches around you, from the sensation of your feet in your shoes to sirens outside. You'd miss new sense signals, too. Many old people continue to have good olfactory function. That's not the rule, however. They'll wake up and smell burned rubber, or a mixture of burned toast and rotten eggs, and they'll have that taste all day.
Breakfast tastes that way, and lunch tastes that way, and dinner tastes that way.
In general, Reed says the most common reasons for olfactory loss are upper respiratory infections and a sharp blow to the head, as in an automobile accident. Unlike hearing or vision, however, the sense of smell can regenerate. It's as if the brain reaches out, sending new nerve fibers down through the plate. The fibers then regrow their proper receptors. The patients are cured.