GHS / HazCom term · Glossary
Respiratory Sensitization
Verified vs OSHA sources · 2026-10-05
A GHS health-hazard class for chemicals that cause hypersensitivity of the airways after inhalation — that is, occupational asthma. Like skin sensitization it has an induction phase, then once a worker is sensitized even very low concentrations can trigger a severe asthmatic reaction. Respiratory sensitizers carry the health-hazard pictogram (GHS08) and the signal word “Danger.”
Also known as: respiratory sensitizer, occupational asthma hazard
Respiratory Sensitization at a glance
- Causes airway hypersensitivity — occupational asthma — after inhalation.
- Induction first, then once sensitized, very low concentrations can trigger attacks.
- Category 1 (sub-categories 1A/1B); pictogram GHS08, signal word “Danger,” H334.
- More severe than skin sensitization (GHS07/Warning) because the reaction is in the lungs.
In plain English
How a label flags a chemical that can give you work-related asthma. After your airways become “primed,” even a whiff can set off serious breathing trouble — which is why it's treated as a more severe hazard than a skin allergy.
What the rule says
“Respiratory sensitization refers to hypersensitivity of the airways occurring after inhalation of a substance or mixture.”
In context
A classification or labeling concept from the UN Globally Harmonized System, adopted into US law through OSHA's Hazard Communication Standard (29 CFR 1910.1200) and its appendices.
Where this is written in OSHA's rules
- 29 CFR 1910.1200 App A.4Read on eCFR / OSHA.gov
Example
Isocyanates (in spray polyurethane foam and two-part paints) are classic respiratory sensitizers. A painter may spray for months, become sensitized, then suffer an asthma attack from a trace exposure. The label carries GHS08, “Danger,” and H334, “May cause allergy or asthma symptoms or breathing difficulties if inhaled.”
Why it matters
Respiratory sensitization can be career-ending and life-threatening — a sensitized worker may react to concentrations far below any exposure limit, so the usual “stay under the PEL” logic isn't enough. Misclassifying or under-labeling one (omitting GHS08/H334) is a serious HazCom failure under 1910.1200.
Respiratory sensitization vs. respiratory irritation
Irritation (e.g., STOT-SE Cat 3, H335) is a direct, dose-dependent effect that eases when exposure stops. Respiratory sensitization is an allergic, immune response — once sensitized, tiny amounts trigger asthma regardless of dose. The sensitizer is the more dangerous and is flagged with GHS08/“Danger.”
Respiratory sensitization at a glance
| Aspect | Detail |
|---|---|
| Hazard class / category | Respiratory sensitization, Category 1 (1A / 1B) |
| Pictogram · signal word | Health hazard (GHS08) · Danger |
| Hazard statement | H334 — May cause allergy or asthma symptoms or breathing difficulties if inhaled |
| Classic causes | Isocyanates, flour / grain dust, some epoxies, certain wood dusts |
Respiratory Sensitization: frequently asked questions
- What is the difference between respiratory and skin sensitization?
- Both are allergic reactions but by different routes. Respiratory sensitization causes airway hypersensitivity (occupational asthma) — GHS08, “Danger,” H334. Skin sensitization causes allergic dermatitis — GHS07, “Warning,” H317. The respiratory hazard is treated as more severe.
- Why is a PEL not enough for a respiratory sensitizer?
- Once a worker is sensitized, an allergic asthma attack can be triggered by concentrations well below the exposure limit. Control relies on minimizing all exposure (engineering controls, substitution), not just staying under a PEL.
- What are common respiratory sensitizers?
- Isocyanates (spray foam, two-part paints), flour and grain dust, some epoxy and acrylate systems, and certain wood dusts. They're flagged with GHS08, “Danger,” and H334.
Related terms
Free tools for this
Governing OSHA standards
More GHS terms
A GHS health-hazard class for the harmful effects that follow a single dose, several doses within 24 hours, or a 4-hour inhalation exposure. Chemicals are sorted into categories by route (oral, dermal, inhalation) using LD50/LC50 cut-offs — Category 1 is the most toxic. OSHA's HazCom standard uses Categories 1–4.
Aspiration HazardA GHS health-hazard class for chemicals that can be fatal if swallowed and then enter the airways — directly or by vomiting — causing chemical pneumonia or lung injury. Thin, low-viscosity hydrocarbons (gasoline, kerosene, lamp oil) are the classic example. It is Category 1, with the health-hazard pictogram (GHS08) and signal word “Danger.”
CarcinogenicityA GHS health-hazard class for chemicals that cause cancer or increase its incidence. GHS (and OSHA's HazCom standard) sorts carcinogens into Category 1A (known human carcinogen), 1B (presumed, from animal evidence), and Category 2 (suspected). Carcinogens carry the health-hazard pictogram (GHS08) and a hazard statement such as H350 (“May cause cancer”).
Chemicals Under PressureA physical-hazard class added by OSHA's 2024 HCS update (aligning with GHS Revision 7) for liquids or solids pressurized with a gas, held in pressure receptacles other than aerosol dispensers and not classified as gases under pressure. It is categorized by the flammability of its contents and always carries the gas-cylinder pictogram (GHS04) for the pressure hazard.
ClassificationThe process of evaluating the available scientific evidence for a chemical against the GHS criteria to decide whether it is hazardous and, if so, the hazard class and category of each effect. Classification is the first step in HazCom — its result determines every label element (pictogram, signal word, hazard and precautionary statements) and SDS content.
Corrosive to MetalsA GHS physical-hazard class for chemicals that, by chemical action, will materially damage or even destroy metals. It is a single category (Category 1), determined by corrosion-rate testing on steel and aluminum, and uses the corrosion pictogram (GHS05) with the hazard statement H290. It is a separate hazard from skin corrosion, even though both use GHS05.
Desensitized ExplosivesA physical-hazard class added by OSHA's 2024 HCS update (GHS Revision 7) for solid or liquid explosives that have been phlegmatized — wetted or diluted — to suppress their explosive properties for safe transport and storage. It has four categories based on the corrected burning rate, and uses the flame pictogram (GHS02), not the exploding-bomb.
Globally Harmonized System (GHS)An internationally agreed framework created by the United Nations (first adopted in 2003) that standardizes how chemical hazards are classified and communicated — using common hazard classes, pictograms, signal words (Danger / Warning), and coded hazard (H) and precautionary (P) statements on labels and safety data sheets. The US adopted GHS into law through OSHA's 2012 Hazard Communication Standard update.
Sources & verification
- 29 CFR 1910.1200 App A.4 (eCFR / OSHA.gov)
- OSHA — Appendix A to §1910.1200: Health Hazard Criteria (Mandatory)
- UNECE GHS — Part 3: Health Hazards
Reviewed by HazComFast against eCFR, OSHA.gov, NIOSH, and the Federal Register. Last reviewed 2026-10-05. This glossary is general information, not legal advice; OSHA State-Plan states (e.g. California, Michigan) may adopt stricter requirements.
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