Open almost any citrus, pine or fresh fragrance oil SDS and you'll find H304 "May be fatal if swallowed and enters airways", the health hazard pictogram and the signal word "Danger". It's the scariest line on the sheet, and makers often assume it has to go on the candle too. It almost never does. It can, however, end up on a reed diffuser, and then it brings packaging rules that catch people out.

What H304 actually means

H304 is the hazard statement for aspiration hazard, Category 1 (Asp. Tox. 1) under the CLP Regulation. It isn't about poisoning. It's about a thin liquid going the wrong way: someone, usually a child, swallows it, and the liquid slips into the windpipe and lungs, either straight away or while vomiting. CLP Annex I, section 3.10, describes the result as severe acute effects such as chemical pneumonia, lung injury or death.

The key property is how runny the liquid is. A pure substance goes into Category 1 on good human evidence, or if it is a hydrocarbon with a kinematic viscosity of 20.5 mm²/s or less, measured at 40 °C. The annex names turpentine and pine oil as examples.

Why it's on so many fragrance SDSs

Citrus and pine notes are built on terpene hydrocarbons: small, oily, very thin molecules. We checked ECHA's records on 29 September 2026:

  • d-Limonene (EC 227-813-5, index 601-096-00-2) has a harmonised Asp. Tox. 1 classification, alongside Flam. Liq. 3, Skin Irrit. 2, Skin Sens. 1B and its aquatic entries.
  • p-Cymene and alpha-terpinene are also harmonised Asp. Tox. 1, and so is turpentine oil.
  • Alpha-pinene (EC 201-291-9) and beta-pinene (EC 204-872-5) have no harmonised entry, but the headline self-classification that ECHA shows for each includes Asp. Tox. 1.

For a mixture such as a fragrance oil, CLP section 3.10.3.3.1.2 sets two conditions, and both must be met:

  • the Asp. Tox. 1 ingredients add up to 10% or more (only ingredients present at 1% or more count), and
  • the mixture itself has a kinematic viscosity of 20.5 mm²/s or less at 40 °C.

A citrus oil can easily be a third limonene, and fragrance oils are thin liquids. So the oil in the bottle gets H304, and because Asp. Tox. 1 carries the signal word "Danger", the whole SDS reads "Danger" even when every other hazard on it is only "Warning".

Why it doesn't reach your candle or wax melt

Your candle fails both conditions.

  • The 10% sum. At a typical load, the Asp. Tox. 1 ingredients are diluted by the wax. To reach 10% in a candle made at a 10% load, the fragrance would have to be made entirely of Asp. Tox. 1 ingredients.
  • The viscosity test. The criterion is a kinematic viscosity measured at 40 °C, and most candle and wax melt blends are still solid at that temperature. CLP also adds a note for substances: although aspiration can in principle involve solids, the viscosity route to Category 1 "is intended to apply to liquid substances and mixtures only".

So a solid candle or wax melt normally carries no H304, no health hazard pictogram from it, and no "Danger" from it. Don't copy them over from the fragrance SDS. The same logic doesn't protect a product that stays liquid, such as a burner oil or a liquid fragrance refill. Those need the same check as a diffuser.

Reed diffusers are different

A reed diffuser is a liquid by design, and it has to be thin enough to travel up the reeds. It also uses far more fragrance than a candle. That puts both conditions within reach.

Take a hypothetical citrus pine oil whose SDS lists 30% d-limonene, 8% alpha-pinene and 4% beta-pinene. That's 42% of Asp. Tox. 1 ingredients.

  • Candle at a 10% load: 3% limonene, 0.8% alpha-pinene, 0.4% beta-pinene. Only limonene reaches the 1% cut-off, so the sum is 3%. Far from 10%, and the candle is solid anyway. No H304.
  • Diffuser at 25% in a base that isn't classified (dipropylene glycol methyl ether, a common diffuser solvent, is headlined "Not classified" on ECHA): 7.5% limonene, 2% alpha-pinene, 1% beta-pinene. The sum is 10.5%. If the finished liquid is at or under 20.5 mm²/s at 40 °C, it's Asp. Tox. 1: H304, the health hazard pictogram and "Danger".
  • Same diffuser at 20%: 6% limonene, 1.6% alpha-pinene, and beta-pinene drops to 0.8%, under the 1% cut-off. The sum is 7.6%, so no H304 from the fragrance.
  • Same oil in an isoparaffin base: hydrocarbon solvents such as "Hydrocarbons, C11-C12, isoalkanes, <2% aromatics" carry Asp. Tox. 1 in ECHA's headline self-classification. At 75% of the bottle, the base alone passes 10%. The fragrance load no longer matters.

The base can decide this more than the fragrance does. Check its SDS as carefully as the oil's.

What H304 means for the bottle, not just the label

If a diffuser sold to the public is classified H304, the label follows CLP Table 3.10.2: the health hazard pictogram, "Danger", H304, and the precautionary statements P301+P310 (if swallowed, immediately call a poison centre or doctor), P331 (do not induce vomiting), P405 and P501. Then CLP Annex II adds two packaging duties:

  • Child-resistant fastening (Annex II, 3.1.1.2): packaging of any capacity supplied to the general public and labelled for aspiration hazard must have one. Reclosable closures must meet EN ISO 8317. The only exception is aerosols and containers with a sealed spray attachment, which doesn't describe a diffuser bottle.
  • Tactile warning of danger (Annex II, 3.2.1.1): aspiration hazard is on the list, so the pack needs a raised warning triangle to EN ISO 11683.

That's a real cost: a standard cork-and-screw-cap bottle may no longer be compliant. Reformulating below 10%, or choosing a base that isn't classified, is often cheaper than retooling the packaging. But decide that before you print labels, not after.

What to take away

  • H304 on a fragrance SDS describes the oil, not your product. Recalculate for what you sell.
  • Candles and wax melts: solid at 40 °C and well under 10%, so normally no H304.
  • Diffusers and other liquids: add up the Asp. Tox. 1 ingredients at 1% or more, including the base. At 10% or more, and thin enough, you need H304, a child-resistant closure and a tactile warning.

Molekule reads the composition from your fragrance and base safety data sheets, checks each substance against ECHA, and applies the 10% sum and the viscosity test to the finished product, next to the pictogram calculations for H317 and H411. Check whether your diffuser needs H304 in Molekule.