SDS section 3 of 16
SDS Section 3: Composition / information on ingredients
Section 3 tells you what the product is made of. For a pure substance it gives the chemical name and identifiers such as the CAS number; for a mixture it lists the ingredients that matter for health and safety together with their concentrations or concentration ranges. A supplier may withhold an ingredient's exact identity only under the trade secret rules.
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What OSHA requires in Section 3
OSHA enforces the content of Section 3 under the Hazard Communication Standard.
Appendix D separates substances from mixtures.
For substances
- Chemical name.
- Common name and synonyms.
- CAS number and other unique identifiers.
- Impurities and stabilizing additives that are themselves classified and contribute to the classification of the substance.
For mixtures
- The chemical name, CAS number or other unique identifier, and concentration of every ingredient that is classified as a health hazard and is either present above its cut-off/concentration limit or presents a health risk below it.
- The exact percentage, unless a trade secret claim is made or there is batch-to-batch variability, in which case concentration ranges may be used.
The standard has a trade secret provision (paragraph (i)). If the chemical identity or concentration is a trade secret, the manufacturer may withhold it, but must state that it is being withheld, must still provide the hazard information, and must disclose it to a treating physician or nurse in a medical emergency. Since the 2024 update, a withheld concentration must be replaced by one of the prescribed ranges listed in paragraph (i), using the narrowest range possible; the trade secrets guide explains the concept in plain language.
GHS Annex 4 and international differences
GHS Annex 4 sets out a similar structure. For substances: chemical identity, common name or synonyms, CAS number and other identifiers, and impurities or stabilizing additives that contribute to the classification. For mixtures: the identity and concentration or concentration range of all ingredients that are hazardous within the meaning of the GHS and present above their cut-off levels. The GHS explicitly allows confidential business information to be protected, in line with national law.
EU SDSs under REACH Annex II usually give more in this section: EC number, REACH registration number and the classification of each listed ingredient. That makes it easier to cross-check the classification. See REACH Annex II SDS format.
What to look for and red flags
What to look for
- For a single substance, a CAS number you can verify against a database. A name without an identifier is hard to confirm.
- For a mixture, the ingredients that drive the hazards in Section 2. Each classified ingredient should be traceable to a hazard statement.
- Concentration ranges. Ranges are common and legitimate; wide ranges can limit how precisely you can judge exposure.
- Stabilizers and impurities, which can change a hazard even when they are present in small amounts.
Red flags
- "Proprietary" or "trade secret" for every ingredient, with no concentration information and no statement about withholding.
- A mixture with a severe hazard classification in Section 2 but no ingredient in Section 3 that could explain it.
- Concentrations that do not add up to a sensible total without explanation (ranges may legitimately overlap or exceed 100% in sum).
- A CAS number that belongs to a different substance than the name beside it.
Worked example: typical fields
An illustrative table for a hypothetical cleaning product (all values are placeholders). For a substance with real identifiers see the composition section of the ethanol page.
| Ingredient | CAS | Concentration | Classification |
|---|---|---|---|
| Named solvent | Valid CAS number | A range, for example 10 to 30% | Hazard class and category |
| Named surfactant | Valid CAS number | A range | Hazard class and category |
| Ingredient withheld as trade secret | Not given | Statement that identity is withheld | Hazard still described in Section 2 |
See how this looks on a real page: ethanol safety data, composition / information on ingredients section. Every chemical page uses these 16 sections with the same anchors, so you can compare any substance.
Common mistakes
- Assuming a short ingredient list means a short hazard list. Only classified ingredients above cut-offs are required, so a non-hazardous majority (often water) may be omitted.
- Searching by trade name instead of CAS number. Names vary by supplier; identifiers do not.
- Using the mixture's percentages as exposure values. They describe the product, not the air you breathe.
- Overlooking residual monomers or impurities. Sometimes a trace component, such as a classified impurity, is the reason for a warning.
- Treating a trade secret claim as an absence of information. Withheld identity does not remove the supplier's duty to describe the hazard.
Frequently asked questions
Does an SDS have to list every ingredient?
No. For mixtures, Section 3 must list the ingredients that are classified as health hazards and present at or above their cut-off levels, plus those that pose a risk below the cut-off. Non-hazardous ingredients may be left out.
Can a manufacturer hide an ingredient on the SDS?
Only under the trade secret provisions. The supplier may withhold the specific chemical identity or exact concentration, must state that information is withheld, and must still describe the hazards. Health professionals can obtain the information in medical emergencies.
Why does the SDS give a range instead of an exact percentage?
Product formulations vary slightly from batch to batch, and ranges are permitted in certain cases. A range is not an error, but check that it is narrow enough to be useful for your risk assessment.
What is a CAS number and why does Section 3 use it?
A CAS Registry Number is a unique numeric identifier for a chemical substance. Section 3 uses it so that you can identify a substance regardless of the different names that suppliers use.