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Learn · Part Two — Learning to resolve · Lesson 5 of 10

Why the components never add up to exactly one hundred

An analysis that adds up to 90 per cent is normal. One that adds up to 99.8 is worth questioning — except for a few oils that are simple by nature.

Add up the percentage column on an essential-oil analysis and you will rarely get exactly one hundred. The figure usually falls somewhere between eighty and ninety-eight.

That is not an error. On the contrary, it is the sign of an honest analysis.

Three places the percentage disappears

Below the identification threshold. A natural essential-oil sample contains hundreds of compounds. Most are at concentrations too low for the machine to separate into distinct peaks, or high enough to show a peak but not enough for mass spectrometry to identify them with certainty.

An honest laboratory leaves them off the list rather than guessing.

Not volatile under the analysis conditions. Plant waxes, some resins and very heavy molecules do not pass through the column. They are in the bottle but not on the analysis.

Overlapping peaks. Two compounds leaving the column at almost the same moment give one merged peak, and depending on the procedure it is either dropped or combined.

Reading the total

Below 80 per cent is a sign worth questioning. Something takes up a significant share without being identified — it may be carrier oil, a very complex sample, or an analysis procedure that is not good enough.

From 85 to 97 is the normal range for most essential oils.

Above 99 is suspicious in the opposite direction. A natural sample is rarely that clean. A figure that round usually means an unusually simple sample — that is, one that may have been built from few ingredients.

Exceptions

A few natural essential oils have one overwhelmingly dominant component and a high identified total. Kaffir lime leaf, with citronellal at nearly eighty per cent, is an example.

For these, a high total is not a bad sign. This is why you have to know the normal range for the species before drawing conclusions from a number.

A detail worth noting

The example page on this site states the identified total and says plainly that the rest lies below the threshold. That is the right way to present it.

An analysis that gives no total, or gives exactly one hundred per cent, has been rounded somewhere. The rounding may be harmless, but you have a right to know it happened.

Further reading for this part

A shared list for the whole of Part Two — Learning to resolve, not a note for every sentence. We state what each source was used for.

  1. Ernest Guenther, 1948–1952. The Essential Oils Six volumes, still the foundation reference for classifying distillation methods. The three-way division we use — water, water and steam, direct steam — comes from here.
  2. International Organization for Standardization. The ISO standards for individual essential oils Each commercial essential oil has an ISO standard setting the ranges for its main components. It is the basis for every statement about a “normal range” in Part Two. The standards must be bought; they cannot be consulted for free.
  3. Robert Tisserand and Rodney Young, 2013. Essential Oil Safety The trade’s standard reference for dilution rates, photosensitisation and contraindications. The figures in this site’s Safety section follow it.

One thing must be said plainly. We have not read every work above in the original; most of the knowledge comes through secondary literature and reviews. We say so rather than let the list suggest a depth of research we have not reached.

Last updated: September 2026