Section 3 of a fragrance safety data sheet lists each hazardous component with a code like "Skin Sens. 1", "Skin Sens. 1A" or "Skin Sens. 1B". They all end in the same hazard statement, H317 "May cause an allergic skin reaction". But the letter after the 1 decides how little of that substance it takes before your candle needs the exclamation mark, or an allergen line. The gap is a factor of ten, and for a few fragrance materials it's a factor of a hundred.

What the categories mean

Under the EU's CLP Regulation, a skin sensitiser is a substance that can cause an allergy after skin contact. CLP Annex I sorts them by how strongly they do it:

  • Sub-category 1A: strong sensitisers. They cause allergy in a high share of people, or at low doses in tests.
  • Sub-category 1B: other sensitisers. Real, but weaker.
  • Category 1: a sensitiser where the data aren't good enough to choose between 1A and 1B. Annex I says a substance goes in plain Category 1 "where data are not sufficient for sub-categorisation".

On the label all three look the same: the exclamation mark pictogram, the signal word "Warning" and H317. The difference is in the thresholds.

The generic limits for your candle

Your candle is a mixture. CLP Annex I, Tables 3.4.5 and 3.4.6, give two limits for each sensitiser in it. The first decides whether the whole candle is classified H317. The second, lower one decides whether the substance must be named on an EUH208 line ("Contains [name]. May produce an allergic reaction") when the candle isn't classified.

  • Skin Sens. 1A: H317 from 0.1% in the candle; EUH208 from 0.01%.
  • Skin Sens. 1B: H317 from 1%; EUH208 from 0.1%.
  • Skin Sens. 1: H317 from 1%; EUH208 from 0.1%.

Notice that plain Category 1 gets exactly the same limits as 1B. In practice, "Skin Sens. 1" without a letter behaves like a 1B substance in your calculation, unless a harmonised entry gives it a specific limit (see below). Citral and geraniol are two common examples: both are harmonised as Skin Sens. 1 in CLP Annex VI, with no specific limit.

Sensitisers are never added together. Each one is compared with its own limits on its own.

Specific concentration limits: when the generic ones don't apply

For some substances, the EU sets a specific concentration limit (SCL) in the harmonised list, CLP Annex VI. When one exists, you must use it instead of the generic limit. For sensitisers it's always lower, because it's reserved for the strongest ones. And the EUH208 limit follows it: Annex I says the elicitation limit is "a tenth of the specific concentration limit".

Two fragrance materials candle makers meet often have one:

  • Isoeugenol (CAS 97-54-1, index 604-094-00-X): Skin Sens. 1A with an SCL of 0.01%. So H317 from 0.01% in the candle, and EUH208 from 0.001%.
  • Cinnamaldehyde, also called cinnamal (CAS 104-55-2, index 606-155-00-6): Skin Sens. 1A with the same 0.01% SCL. Its harmonised entry was added by Delegated Regulation (EU) 2024/197 and has applied since 1 September 2025.

Compare that with linalool, harmonised as Skin Sens. 1B with no SCL: it needs 1% in the candle for H317. Isoeugenol needs a hundredth of that.

A worked example at 10% fragrance load

Take four hypothetical fragrance oils. Each contains 0.5% of one sensitiser, and nothing else that matters here. You use each at a 10% load, so the finished candle holds 0.05% of that sensitiser. Same amount, four different labels:

  • Oil A, citral (Skin Sens. 1): 0.05% is under the 0.1% EUH208 limit. Nothing on the label from citral.
  • Oil B, linalool (Skin Sens. 1B): same result. 0.05% is under 0.1%, so nothing on the label.
  • Oil C, a 1A substance with no SCL (for example one your supplier self-classifies as 1A): 0.05% is over the 0.01% EUH208 limit but under the 0.1% classification limit. EUH208 line, no pictogram.
  • Oil D, isoeugenol (Skin Sens. 1A, SCL 0.01%): 0.05% is five times its SCL. The candle is classified H317: exclamation mark, "Warning", the H317 statement and its precautionary statements, with isoeugenol named on the label.

Now raise each oil's sensitiser to 2%, so 0.2% in the candle. Citral and linalool now reach 0.1% and move onto the EUH208 line, still with no pictogram. Oil C crosses 0.1% and gets H317. Oil D was already there.

And go the other way. If Oil D held only 0.01% isoeugenol, the candle would hold 0.001%. That's still enough for an EUH208 line naming isoeugenol. A trace that looks irrelevant on the SDS still reaches your label.

What to check on your fragrance SDS

  • Read the letter, not just "Skin Sens." 1A versus 1B is a factor of ten in both limits.
  • Look for an SCL. Section 3 of a good SDS lists specific concentration limits next to each component. If it shows "C ≥ 0.01%" for H317, use that number, not the generic one.
  • Check harmonised entries yourself. A harmonised classification in Annex VI overrides a supplier's own. An SDS printed before September 2025 may still show cinnamaldehyde without its 1A classification and SCL.
  • Watch the low-percentage lines. Components listed at "<0.1%" are exactly where 1A substances with an SCL can hide.

Molekule reads every component from your fragrance SDS, checks its sub-category and any specific limit against ECHA's live data, and applies the right thresholds at your load for your candles. Check which sensitisers reach your candle label in Molekule.