Hydrogen cyanide is a highly toxic volatile nitrile best known as the acute hazard associated with cyanogenic materials rather than as a beneficial aroma constituent. In the AromaForge archive it appears in bitter almond context as a tightly limited trace impurity or assay target, not as a wellness-facing molecule. The evidence base here is strong for identity, toxic mechanism, occupational exposure concern, and emergency guidance, so this record should stay explicitly safety-first and avoid any promotional framing.
Chemical identity and composition
PubChem identifies hydrogen cyanide as formonitrile with formula CHN, while PubChem synonym data and OSHA list hydrocyanic acid and prussic acid as standard alternate names. ATSDR and NIOSH describe it as a colorless or pale-blue liquid below about 78 F and a volatile gas above that range. In local archive data, bitter almond oil context lists hydrocyanic acid at up to 0.01%, reinforcing that this constituent is relevant mainly as a trace safety marker.
Aroma and practical use
- Use the recorded bitter-almond-like descriptors to explore a blend's scent character; perceived strength also depends on the other ingredients.
- Read the route, preparation and experimental context before using a study finding to choose an oil.
Reported benefits and effects
Findings retain their study context. An animal or laboratory result describes that experiment.
A 1980 occupational study found that workers exposed to cyanide fumes and aerosols had much higher blood and urine cyanide and thiocyanate concentrations than controls, and workers reported typical hydrogen-cyanide poisoning complaints even at measured workplace values the authors considered low.
The abstract reports breathing-zone cyanide up to 0.8 mg/m3 and workroom atmosphere up to 0.2 mg/m3, with the authors arguing that the applicable maximum allowable concentration should be reviewed for their setting.
Apply this finding only to the studied preparation, participants, route and outcome. It does not establish the same result for a custom oil blend.
A 2017 cassava-processing study measured chronic occupational hydrogen-cyanide exposure in Brazilian flour houses at average TWA levels of 0.464 to 3.328 mg/m3 and found urinary thiocyanate evidence consistent with high exposure in the studied population.
The abstract notes that these levels were below a 5 mg/m3 TLV-C but not below a 2.5 mg/m3 action level, and the authors interpreted the data as a possible risk for susceptible individuals.
Apply this finding only to the studied preparation, participants, route and outcome. It does not establish the same result for a custom oil blend.
A 2006 petrochemical-complex risk assessment identified hydrogen cyanide as one of the substances contributing to chronic noncancer hazard indices above 1 for exposed workers in that industrial setting.
The study evaluated 39 air toxics across 11 companies and concluded that multiple emission sources, including hydrogen cyanide, contributed to potential excess noncancer risk.
Apply this finding only to the studied preparation, participants, route and outcome. It does not establish the same result for a custom oil blend.
Use concerns and concentration limits
Sensitization concernNot flagged
Not flagged in the current model. This is not proof of absence or unrestricted safety.
Phototoxicity concernNot flagged
Not flagged in the current model. This is not proof of absence or unrestricted safety.
Oxidation concernNot flagged
Not flagged in the current model. This is not proof of absence or unrestricted safety.
Penetration enhancementNot flagged
Not flagged in the current model. This is not proof of absence or unrestricted safety.
No numeric constituent-specific use limit is available here. Missing is not an unrestricted-use clearance.
NIOSH states that hydrogen cyanide interferes with the body's use of oxygen and that exposure can be fatal.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
No direct public citation is attached to this entry.
OSHA lists a ceiling permissible exposure limit of 10 ppm with skin notation, while NIOSH and OSHA both list an IDLH value of 50 ppm in the reviewed materials.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
No direct public citation is attached to this entry.
ATSDR states that symptoms can begin within seconds to minutes after inhalation, dermal absorption can contribute to systemic poisoning, and odor is not a reliable warning because a substantial fraction of people cannot detect it.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
No direct public citation is attached to this entry.
ATSDR medical management guidance and a New Jersey Right to Know Hazardous Substance Fact Sheet describe dermal/ocular contact with hydrogen cyanide as causing irritation and rapid systemic absorption (with poisoning risk), not allergic contact sensitization; no source reviewed in this pass classifies hydrogen cyanide as a skin sensitizer.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
No direct public citation is attached to this entry.
Constituents it may interact with
No constituent-pair interaction is recorded for this identity. The report does not assume either amplification or incompatibility.
How the effects were investigated
cellular asphyxiant via cytochrome oxidase inhibition
ATSDR and the NCBI AEGL monograph describe hydrogen cyanide as a cellular asphyxiant that binds mitochondrial cytochrome oxidase and prevents normal oxygen utilization in cellular metabolism.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
detoxification to thiocyanate
The AEGL monograph states that cyanide is metabolized by rhodanese, which transfers sulfur to cyanide to form the relatively less toxic thiocyanate.
The source assessment applies to its specified exposure and preparation; this entry is not an unrestricted-use clearance.
What this report cannot establish
- A reported constituent percentage does not establish an effective human therapeutic dose or the amount absorbed into the body.
- The presence of a constituent does not guarantee a clinical benefit, rash treatment or sleep improvement from a custom blend.
- An unflagged concern or missing use limit does not establish safety for ingestion, inhalation, skin exposure or a particular person.
- A candidate constituent interaction does not establish that two oils amplify one another at the selected proportions.
- Constituent descriptors alone do not establish a precise top, heart or base lifetime in a finished blend.
Known data gaps (7)
- This record intentionally emphasizes toxicology and exposure control rather than wellness-oriented literature because that is where the evidence is strongest and most appropriate.
- No aroma-benefit or consumer-use efficacy literature was sought because such framing would be misleading for hydrogen cyanide.
- The local oil-context figure is a trade-journal assay value rather than a broad market survey of bitter almond oils.
- No fragrance-industry (IFRA/RIFM/Tisserand) dermal percentage limit exists for hydrogen cyanide because it is not used as a deliberate fragrance ingredient; the previously listed 0.1% dermal_limit_pct was an unsourced placeholder and has been cleared to null in this pass. OSHA lists a 10 ppm ceiling PEL with skin notation and NIOSH recommends a 4.7 ppm (5 mg/m3) 10-minute ceiling for occupational air exposure, but these are air-exposure limits, not a comparable topical cosmetic dermal limit.
- Second-pass 2026-07-13 retry deliberately did not force an IFRA-style dermal_limit_pct given the acute-toxic-gas nature of this constituent; instead it searched for essential-oil-context corroboration. A PMC-indexed 2016 paper on extraction, chemical composition, and antifungal activity of bitter almond essential oil, together with commercial supplier documentation (e.g., Eden Botanicals bitter almond product page), confirms that bitter almond essential oil is conventionally rectified/redistilled specifically to remove prussic acid (hydrogen cyanide) before sale, and that unrectified bitter almond oil is not considered safe. This corroborates the existing framing (trace/decomposition constituent, not a deliberate fragrance ingredient with an IFRA dermal limit) but does not establish any authoritative percentage-based dermal limit; fields remain null/false as before.
- No constituent-specific numeric dermal reference is available here.
- Some findings do not record an explicit exposure route; consult the linked study before applying them to a use.