I read a wonderful piece of misinformation recently telling how a perfume is composed of over 1,000 ingredients. I suspect that the writer mistook the number of ingredients that are available to the perfumer today (although the number now probably lies between three and five thousand) with the number of ingredients that a perfumer might actually USE in a particular perfume.
As to the number of ingredients that might really be used in a perfume, there is no set number. Not even a "suggested" number. The perfumer uses as few or as many materials as are needed to create the desired perfume. Mid-19th century perfumes were often composed with six or fewer ingredients. 20th and 21st century fragrance, on occasion, might make use of more than 100 ingredients -- or less than thirty.
For the perfumer working with a good sense of smell but limited resources, formulas are likely to be made up of fewer ingredients for a simple TECHNICAL reason -- the difficulty of accurately adding very small amounts of a material to a formula.
For example, I have a fragrance, "Manama" (www.PGLightyears.com/Manama.shtml), that uses fewer than 25 ingredients. And, of these ingredients, some are in large proportion and some -- while important -- are used quite sparingly. If I take the Manama formula and run it through Steve Dowthwaite's "Perfumer's Workbook" software (www.perfumeprojects.com/store/1013.shtml) and ask the software to give me "25% more depth," the software will suggest ingredients that might be added to the formula BUT, for some, the suggested addition is SO SMALL that I would have no way to measure it with the equipment I have on hand.
In the case of "Manama," the software suggests the addition of 0.0003 grams of Oakmoss Absolute. But my scale measures only down to a thousandth of a gram. Sure, I could scale up the formula and make a large batch of this experimental version to see if I like it any better. But as one of the ingredients is Rose de Mai absolute, the COST of this experimentation would be prohibitive.
So like so many others in my situation, using trace amounts of aroma chemicals in a formula becomes problematic. Does it matter? Jacques Guerlain was known for creating wonderfully complex formulas -- "Shalimar" for example. But his wife was said to favor Francois Coty's perfumes -- simple perfumes that used just a handful of ingredients and were created by a man who had spent just one year in perfume school. Jacques Guerlain had grown up in the family perfumery and had been trained by his distinguished uncle, perfumer Aime Guerlain.
For the person who works as I do, in order to get particularly small amounts of an ingredient into a perfume, we would mix that item with DPG (Dipropylene Glycol), an almost odorless solvent that will "cut" many aroma materials without greatly altering their aroma or the aroma of the compound in which they are used. Thus I might mix, by weight, one part of an aroma material that interests me with nine parts DPG, or even one part of a very strong aroma material with 99 parts DPG.
From personal experience I can attest that this method is very practical, although weighing out your materials still requires a good scale (electric "balance"), a steady hand and a good quality dropper or disposable plastic pipette.
Using this technique, even when you are working with small batches of fragrance, you CAN make use of relatively small amounts of aroma materials to round out, smooth out, or decorate your fragrance but you do have to be aware of the limitations in accuracy of your hand, your dropper or pipette, and your scale.
So how many ingredients does it take to make a perfume? It's all up to the creative vision and technical skill of the perfumer.
As a final note, this technique of diluting perfumery materials to get a weaker solution is not new. Perfumers have been doing it for well over 100 years.