Bad smells are not necessarily bad for you, says air-pollution expert Timothy Buckley. Some stenches are harmless, while some killers, such as carbon monoxide and radon, have no scent.

Unpleasant and Dangerous

Auto exhaust: When you’re stuck in traffic, you’re inhaling deadly chemicals, including carbon monoxide, benzene, and soot.

Gasoline: Don’t linger near the pump. Gas fumes contain carcinogens and toxins.

Sewage plants: That foul breeze may contain illness-inducing bacteria, endotoxins, and chemical irritants.

Tar: It smells nasty, and it is. Hot tar contains polycyclic aromatic hydrocarbons, suspected carcinogens.

Just Unpleasant

Chlorine: The air around swimming pools and hot tubs can irritate your eyes and throat, but it’s not toxic.

Garbage: Distasteful, yes; harmful, no.