It’s time for a romantic night out with that special someone. Deodorant? Check. Cologne or perfume? Check. Brushed teeth? Check.

Minty fresh breath? Better ask your date.

That’s because self-detection of bad breath is notoriously difficult. Often, a person won’t know they have halitosis unless somebody tells them. And how embarrassing is that? This issue can be more serious than just scaring someone away. Bad breath also can be a sign of a serious medical or dental problem.

Chemists think they’ve got a solution — the halitosis detector.

The source of bad breath is hydrogen sulfide, a colorless gas that, when there is enough of it, smells of rotten eggs. It’s poisonous and flammable and can kill you. In fact, volcanoes spew it.

Hydrogen sulfide can be expelled from your mouth, too, creating bad breath. In a volcano, magma produces the gas. In our mouths, it’s bacteria.

Why doesn’t our bad breath kill us, or at least allow us to shoot flames from our mouth like a dragon? People with halitosis expel too little of it — up to 2 parts per million. So, how do you detect such a small amount of the gas?

In a recent paper, those tinkering chemists describe creating a sensor using lead acetate, which reacts with hydrogen sulfide. The chemists anchored the lead acetate in a 3-D nanofiber web. Blow into it, and the resulting reaction, if the person has bad breath, turns the web brown in a minute.

The detector isn’t on store shelves just yet, but the researchers envision an eventual portable halitosis detector that doctors could use.

In a sense, it works like an over-the-counter pregnancy test, except the result isn’t a bundle of joy.