Hydrogen Cyanide (HCN)

What is Hydrogen Cyanide (HCN)?

Hydrogen cyanide (HCN, prussic acid) is a colourless gas with a characteristic bitter-almond smell — though only about 60 percent of people can detect it due to genetic variation. HCN is acutely highly toxic because it blocks cellular oxygen utilisation in mitochondria. In cigarette smoke it forms during combustion of nitrogen-containing tobacco components.

Why is Hydrogen Cyanide (HCN) in cigarettes?

Tobacco leaves contain plenty of nitrogen in the form of amino acids, nicotine and plant proteins. Incomplete combustion of these compounds produces hydrogen cyanide. Each cigarette delivers 150 to 300 micrograms of HCN into the mainstream smoke (source: DKFZ). Acute poisoning doses are far higher — a single cigarette won't kill anyone — but regular inhalation chronically deprives airway cells of function.

What Hydrogen Cyanide (HCN) does to your body — short term

Hydrogen cyanide blocks cytochrome-c-oxidase in mitochondria — the enzyme that lets cells convert oxygen to energy. Cells effectively drown in oxygen they can't use. At cigarette-smoke quantities this causes no noticeable acute symptoms, but every puff temporarily halts oxygen utilisation in bronchial cells. Repeated every few hours over years, the damage adds up.

What Hydrogen Cyanide (HCN) does long term

Chronic hydrogen cyanide exposure from tobacco smoke contributes to damage of the bronchial cilia — the same self-cleaning function impaired by tar. There's also a long-term contribution to endothelial damage and thus atherosclerosis. Studies show measurable neurological effects (concentration weakness, vision disturbances) in heavy smokers, partly attributed to HCN.

How it compares

Germany's workplace exposure limit for hydrogen cyanide is 11 mg/m³ (10 ppm, DFG MAK 2023) — set to handle acute toxicity, not chronic damage from low continuous intake. A pack-a-day smoker inhales roughly 4 milligrams of HCN per day — as highly concentrated bursts directly into the bronchi, without the dilution of a fresh-air-supplied workspace.

Workplace exposure limit: 11 mg/m³ (10 ppm, DFG MAK 2023)