What Is Odor Threshold, and Why Does Less Sometimes Mean More?
Odor threshold is the lowest airborne concentration at which a molecule can be detected by the human nose. A material with a low threshold announces itself even in trace amounts. One with a high threshold can be present in large quantities and still recede into the background. In a formula, the question is not "how much did you add?" but "how much can the nose actually perceive?"
That is why a single drop can determine the fate of an entire formula. A low-threshold thiol or aldehyde can topple a carefully built balance on its own. The rest is hidden in your scales.
Low- and High-Threshold Materials: A Practical Map
The table below is not definitive laboratory data — it is workshop intuition. Threshold values vary from source to source; keep relative strengths in mind as you work with your own raw materials.
| Material type | Relative odor threshold | Practical dosage behaviour |
|---|---|---|
| Thiols / sulphurous notes (blackcurrant, roasted) | Very low | Used at trace levels (ppm range); excess ruins the blend |
| Aldehydes | Low | Delivers noticeable brightness even at 0.1–1% |
| Strong florals (jasmine lactones, indole) | Low–medium | Start small and increase in increments |
| Citrus volatiles (limonene etc.) | Medium–high | Require generous dosage but evaporate quickly; longevity should not be expected |
| Musk, amber, woody fixatives | High | Used at high percentages; linger on-stage for a long time |
Dosage Optimisation: A Step-by-Step Approach
Correct dosage is not about finding the "right ratio" in one go — it is about approaching the threshold gradually. Tame a potent material first with a stock solution (dilution), then transfer it to your formula.
- Prepare a stock solution
Never add a low-threshold material directly to a formula. First prepare a 1% or 10% solution (for example, by diluting the material in perfumer's alcohol). This lets you control the impact of a single drop.
- Start at a trace dose
Add a small amount of the stock solution to the formula. Blend, smell, and take notes. With a powerful material, "too little" can always be corrected; "too much" cannot be undone.
- Increase in increments
If perception has not yet emerged, raise the dose gradually. The moment you cross the threshold you will hear the note; mark that point.
- Balance within the accord
When the material you tested in isolation is placed inside an accord, its behaviour changes. Account for the masking effect of other notes. See How to Build an Accord: Raw Material Weight Balance.
- Rest and re-evaluate
Smell the formula after maceration (room temperature ~15–20 °C, protected from light) and cold filtration. Once the initial alcohol blast has subsided, the true dosage perception becomes clearer; sometimes a material that seemed excessive early on settles into place.
Common Threshold and Dosage Mistakes
Most aspiring formulators attribute potency to ratio. Yet the nose responds to concentration, not ratio. Here are the traps that come up time and again.
Summary and Frequently Asked Questions
Threshold is the invisible scale of formulation. A low-threshold material appears larger than its quantity suggests; a high-threshold material stays quiet even in generous amounts. Correct dosage begins with recognising this invisible measure. When the top note has lifted, the balance you have built takes the stage.
Why does a note dominate the entire composition even when I've used very little of it?
Will using a low-threshold material make my fragrance more long-lasting?
Can you give me a single definitive figure for the "correct dosage" of a potent material?
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