What would cause someone's farts to stop stinking?

Say if you lived 18 years with horrific gas, and then…they suddenly stop smelling it has continued to do so for the last 10 years, what would cause such a thing?

No changes in diet. No more or no less episodes of flatulence per day than usual.

The stuff in their guts (enzymes/bacteria) that made the foul smell were eaten by bigger/meaner organisms that don’t produce the same odor?

Olfactory nerve damage?

Yeah, you finally burned your nose out?

Rather like the old joke: A aged couple are sitting in church. The wife whispers to her husband, “I just passed gas silently. What should I do?” The husband says, “You should change the batteries in your hearing aid.”

Charcoal underpants.

Flower diet?