Parfum, Eau de Parfum, Eau de Toilette, Eau de Cologne. The four names on a label describe how much perfume concentrate is dissolved in alcohol: Parfum is the strongest, usually around 20 to 30 percent; EDP around 15 to 20; EDT around 5 to 15; Eau de Cologne around 2 to 5.
Four words on four bottles
Four bottles carry the same name and stand side by side on a shelf, differing only in a small line of text under the name. That line refers to concentration: the percentage of perfume concentrate in the solution. In the usual language of the perfume trade, Parfum, also called Extrait, is the strongest; Eau de Parfum (EDP) comes second; Eau de Toilette (EDT) is lighter; Eau de Cologne (EDC) is the most dilute. The percentage ranges attached to them are an industry convention, not a legal standard.
So the question of how EDP and EDT differ has a short answer. EDP holds more concentrate, so the scent is usually denser and stays on skin longer than EDT. The longer answer rests on three points: the figures are only ranges, each house sets its own level, and under one perfume name the EDT may be a different formula rather than the EDP with more alcohol.
All four names are French and come from different periods. Eau de Cologne is the oldest of the group, tied to a style of citrus water from the city of Köln in the early eighteenth century. The others came into wide use later, as the perfume trade needed to separate several strengths of the same scent.
In practice a perfume house rarely issues all four versions of every name. Some names exist only as EDP. Some exist as EDT and Parfum. The small line under the name is the first clue to which of these is in hand.
Concentrate in alcohol
A bottle of perfume has two parts. The first is the perfume concentrate, called jus in the trade: the blend of essential oils, extracts and aroma molecules a perfumer builds into a formula. The second is the solvent, usually perfumer's alcohol, a high-strength ethanol denatured under each country's rules, sometimes with a little water.
Alcohol does two jobs. It dissolves the concentrate into a clear solution, and on skin it evaporates very fast, carrying the lightest molecules to the nose first. That is why the first seconds after spraying often smell of alcohol. The alcohol leaves; the scent stays.
The ratio between these two parts is what the words EDP and EDT describe. Roughly by volume, a 100 ml bottle at 15 percent holds about 15 ml of concentrate; at 5 percent, about 5 ml. The conversion can be tried on the library's formula calculator, where 20 percent is marked as EdP strength.
After mixing, the solution usually rests for days to weeks, a stage called maceration, before chilling and filtering until clear. The process is a distant relative of the tincture, where material is steeped in alcohol and the solvent is not removed. The difference lies in what goes in: a tincture extracts one raw material, while a perfume dissolves a finished formula.
The usual ranges
The figures below are the ranges most often quoted in trade literature and reference works. They differ by a few points between sources, and that difference is the first thing worth noting.
Parfum or Extrait is usually quoted at around 20 to 30 percent concentrate; some sources lower the floor to 15. Eau de Parfum is around 15 to 20 percent. Eau de Toilette is around 5 to 15 percent, often near 10. Eau de Cologne is around 2 to 5 percent. Eau Fraîche, where it appears on a label, is usually 3 percent or less.
Eau de Cologne has two meanings. The first is a citrus and herbal style made by Johann Maria Farina in Köln from 1709, a structure discussed in the piece on the cologne accord. The second is simply the most dilute strength. A bottle labelled Eau de Cologne today may mean one, the other, or both.
A higher concentration does not make a scent proportionally louder. The nose does not add smells like numbers, and every molecule has its own odour threshold, with differences of several orders of magnitude. What concentration changes most clearly is time. In an EDT the top notes carry most of the impression; in a Parfum the woods, resins and musks have more material to remain. The library's volatility chart shows this pace oil by oil: citrus leaves a blotter within hours, woods and resins stay for days.
No common law for the names
A perfume label sold in Europe must list its ingredients, and the whole fragrance part is grouped under one word: parfum. Fragrance allergens above set thresholds must be named individually. The concentration of the concentrate need not be. No common provision defines EDP, EDT or Parfum by a number.
So each house sets its own level. One house's EDT can be as strong as another's EDP. Two houses both writing Extrait may sit five or ten percentage points apart. The real figure is known only when the maker publishes it, and most do not.
Beyond the four familiar names, the market uses many more words: Eau Fraîche, Intense, Elixir, Absolu. These have no common definition either. Sometimes they indicate strength, sometimes a new formula under an old name, as the piece on flankers records.
None of this makes the figures worthless. They are a shared language between perfumers, makers and sellers, enough to give direction. Reading them as a direction, not a measurement, is the reading closest to how the trade actually works.
Why an EDT is not just a thinner EDP
A formula balanced at 18 percent does not balance itself at 8 percent. On dilution, materials do not weaken evenly. A molecule with a very low odour threshold stays clearly perceptible, while one that needs a large amount to register falls back. The perceived balance between tiers shifts, even though the ratio on paper stays the same.
So perfumers usually revisit the formula when changing strength. Some houses keep the formula nearly intact and change only the alcohol. Some rebuild part of it, altering the top or the base. Some make an almost new formula and keep only the name and the general idea.
The third case is not rare. Wikipedia notes that some perfumes sharing a name at different concentrations use altogether different concentrate blends, and cites a classic perfume whose Parfum, EDP and EDT are separate compositions. Three words on three labels may therefore name three related scents, not one scent at three strengths.
The practical consequence is that one version cannot be inferred from another. Comparing an EDP and an EDT of the same name means smelling both, on skin or on a blotter, over several hours. The difference is often clearest after the first hour, once the alcohol and the top notes have gone.
Perfume in oil
Not every perfume uses alcohol. The concentrate can be dissolved in a non-volatile carrier oil such as jojoba or fractionated coconut. The result is a denser liquid, applied with a roller or a dipstick rather than sprayed.
Oil changes the way scent leaves skin. With no alcohol lifting off in the first seconds, the opening is softer and travels less; the scent stays closer to the skin. The names EDP and EDT do not apply to this form. Makers usually state the percentage of concentrate in the oil, or state nothing.
The attar tradition of India and the Middle East is another branch: flowers or plant material are distilled into a sandalwood oil base, which holds and carries the scent. Here the line between concentrate and solvent blurs, because the base itself has an odour.
For a blend of essential oils made at home, in oil or in alcohol, the percentage takes a more concrete meaning: it is the amount of essential oil actually in contact with skin. Each oil has its own limit listed on its library page, and the total must be set by the strictest one. The piece Alcohol, time and darkness continues with dilution and maceration.
The four words on a label measure a ratio, not a scent.
One name can hold four formulas.
The rest appears after the first hour, on skin.