Lethal Dose 50 — the single dose that kills 50% of a test population, expressed in mg per kg of body weight. It's used to classify acute oral and dermal toxicity.

Does a lower LD50 mean more toxic?

Yes. A lower LD50 means a smaller dose is lethal to half the test population, so the substance is more toxic. LD50 is also not a safe dose — it's a lethality benchmark.

What are the LD50 toxicity categories?

Under HazCom, oral LD50 cut-offs are: Category 1 ≤ 5 mg/kg (most toxic), Category 2 > 5–50, Category 3 > 50–300, and Category 4 > 300–2000 mg/kg.

GHS / HazCom term · Glossary

LD50

Verified vs OSHA sources · 2026-10-05

Lethal Dose 50 — the single dose of a substance that kills 50% of a test population, expressed in milligrams of substance per kilogram of body weight (mg/kg). It's used to classify acute oral and dermal toxicity. A lower LD50 means a more toxic substance: it takes less to be lethal. Under HazCom, oral LD50 cut-offs define Categories 1 (≤ 5 mg/kg, most toxic) through 4 (≤ 2000 mg/kg).

29 CFR 1910.1200 App A.1

Also known as: lethal dose 50, median lethal dose

LD50 at a glance

Measures oral/dermal lethality — the dose killing 50% of a test population.
Expressed in mg/kg of body weight.
Lower LD50 = more toxic.
HCS oral cut-offs: Cat 1 ≤ 5, Cat 2 > 5–50, Cat 3 > 50–300, Cat 4 > 300–2000 mg/kg.

In plain English

The amount of a substance (per unit of body weight) that would kill half of a test group in a single dose. Smaller number = more poisonous, because it takes very little to be deadly. A pinch that's lethal is far worse than a whole spoonful.

What the source says, in summary

Acute toxicity refers to those adverse effects occurring following oral or dermal administration of a single dose of a substance ... [classified via the LD50].
29 CFR 1910.1200 App A.1.1Summarized, not quoted: read the source for its operative wording.

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.

29 CFR 1910.1200

Where this is written in OSHA's rules

29 CFR 1910.1200 App A.1Read on eCFR / OSHA.gov

Example

A pesticide with an oral LD50 of 3 mg/kg is HCS Category 1 — the most severe band, which ends at 5 mg/kg — while table salt's LD50 (~3,000 mg/kg) sits beyond Category 4, whose upper bound is 2,000 mg/kg. Scale it to a 70 kg adult: 2 grams works out to about 29 mg/kg — a rounding error against salt's lethal dose, and nearly ten times the pesticide's.

Why it matters

LD50 anchors acute oral and dermal toxicity classification, which sets the label's pictogram (skull-and-crossbones for the top categories), signal word, and first-aid statements. It also lets safety pros compare the relative deadliness of chemicals on one common scale — critical when substituting a less toxic alternative.

A lower LD50 is MORE dangerous

The counterintuitive part: a smaller LD50 number means greater toxicity, not less. LD50 is also not a “safe dose” — it's the dose lethal to half a test population. Real exposure limits (like PELs) are set far below any lethal figure.

HCS oral acute toxicity categories (by LD50)

Category	Oral LD50 (mg/kg)	Toxicity
1	≤ 5	Most toxic
2	> 5 to 50	High
3	> 50 to 300	Moderate
4	> 300 to 2000	Lower

LD50: frequently asked questions

What is LD50?: Lethal Dose 50 — the single dose that kills 50% of a test population, expressed in mg per kg of body weight. It's used to classify acute oral and dermal toxicity.
Does a lower LD50 mean more toxic?: Yes. A lower LD50 means a smaller dose is lethal to half the test population, so the substance is more toxic. LD50 is also not a safe dose — it's a lethality benchmark.
What are the LD50 toxicity categories?: Under HazCom, oral LD50 cut-offs are: Category 1 ≤ 5 mg/kg (most toxic), Category 2 > 5–50, Category 3 > 50–300, and Category 4 > 300–2000 mg/kg.

Free tools for this

HazCom Audit Checklist (2026)

Governing OSHA standards

OSHA Hazard Communication Standard (HazCom)

More GHS terms

Acute Toxicity

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 Hazard

A 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.”

Carcinogenicity

A 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 Pressure

A 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.

Classification

The 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 Metals

A 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 Explosives

A 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

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.

Put LD50 into practice

Don't just read the definition — apply it. Use the free HazCom Audit Checklist (2026) to put real numbers behind LD50 for your jobsite.

Get the Binder in Order Before the Inspector Arrives. Are You Ready?

OSHA does not give advance notice of inspections (29 CFR 1903.6). Get the binder in order before the opening conference, not during it.

Serious Violation

$16,550

per violation (max)

HazComFast Pro

$199/mo

10 jobsites, unlimited chemicals, unlimited workers

Use the free tools View Pricing

New sign-ups are paused. The free tools below need no account, and customers can log in as usual.

Your account keeps working as usual. Cancel anytime.