Diethyl phthalate, CAS number 84-66-2, is a colourless liquid with almost no smell. For decades it sat in countless perfume bottles without anyone smelling it. The word phthalate is now often followed by worry; this essay takes that word apart into named substances.
A scentless substance in a bottle of scent
A bottle of perfume does not hold only odorous molecules. It also holds substances with other jobs: dissolving thick materials, keeping molecules evenly distributed, slowing the fast evaporating part. Such substances are best without a smell, so that they do not intrude on the formula.
Diethyl phthalate, DEP for short, is one of them. It is a colourless liquid with no significant odour and a bitter taste. According to the US Food and Drug Administration's page on phthalates in cosmetics, DEP is used as a solvent and fixative in fragrances. A 2009 study in PLoS ONE notes that DEP may also be used to denature alcohol, for example alcohol intended for cosmetics.
Because it has no smell, DEP is not chosen for itself. It is chosen for what it does to other substances. That is also why it is rarely mentioned in the description of a perfume, and usually comes up only when there is a question about safety.
That question is real and deserves an answer in terms of named substances. The word phthalate does not refer to one substance but to a whole family, and members of that family are assessed very differently.
Phthalates are a family, not a substance
Phthalates are esters of phthalic acid. Each phthalate is a benzene ring carrying two ester groups, and those two groups come from an alcohol. Change the alcohol and the substance changes: methanol gives dimethyl phthalate (DMP), ethanol gives diethyl phthalate (DEP), butanol gives dibutyl phthalate (DBP), 2-ethylhexanol gives bis(2-ethylhexyl) phthalate (DEHP).
The family's largest use lies outside cosmetics: softening plastics, above all PVC. Phthalates made from alcohols of seven to thirteen carbons hold the main position as general purpose plasticisers. Phthalates from alcohols of one to three carbons, such as DMP and DEP, are not used as PVC plasticisers; they are lighter and serve as fixatives in perfume.
The difference in molecular size brings differences in how the body handles them and in the results of toxicity testing. So regulators do not assess phthalates as a block. They assess each substance, and reach different conclusions for each.
When an article says phthalates are harmful, the first question to ask is: which phthalate, at what dose, by what route. Many widely cited studies concern DEHP in plastics or mixtures of several phthalates in the environment. They do not automatically speak to DEP in a bottle of perfume.
DEP and its role as a solvent
In a perfume DEP does two jobs. It dissolves thick or crystalline materials so that they mix evenly with the rest. And because it evaporates slowly, it holds part of the odorous molecules on skin for longer, the role the trade calls fixing.
In 2001 Api published in Food and Chemical Toxicology a review of DEP in its role as a solvent and vehicle for fragrance and cosmetic ingredients. The review covers acute toxicity, eye and skin irritation, skin sensitisation, phototoxicity, absorption through skin, metabolism, reproductive toxicity, estrogenic potential, genetic toxicity and carcinogenicity. Its conclusion: no toxicological endpoints of concern were identified, and the estimated exposure from cosmetics, 0.73 mg/kg per day, indicated no significant risk.
In the United States, the Cosmetic Ingredient Review expert panel reaffirmed in 2002 its 1985 conclusion that DBP, DMP and DEP are safe as used in cosmetics. The FDA page, updated on 19 May 2022, states that the FDA does not have evidence that phthalates as used in cosmetics pose a safety risk. The same page records that phthalate use in cosmetics decreased considerably from 2004 to 2010, and that by a 2010 survey DEP was the only phthalate still in common use.
The picture does not stand still. A 2020 systematic review in Environment International of animal toxicology studies on DEP notes that DEP has generally not been found to share the antiandrogenic mode of action common to other phthalates, but that there is emerging evidence it may be associated with other kinds of effect, and it calls for further assessment. Reading the literature correctly means holding both statements at once.
The phthalates banned in EU cosmetics
At the other end of the phthalate family stand DEHP and DBP. DEHP is classified as toxic to reproduction, category 1B. In 2008 it was added to the REACH list of substances of very high concern, and in 2011 to the list of substances requiring authorisation. Since 7 July 2020, entry 51 of Annex XVII of REACH has limited DEHP, DBP, BBP and DIBP to 0.1 percent by weight of the plasticised material in all articles placed on the EU market.
For cosmetics, EU law has a general principle: substances classified as carcinogenic, mutagenic or toxic to reproduction in categories 1A and 1B are banned, save narrow exceptions. DBP, once used as a plasticiser in nail polish, is banned in EU cosmetics, nail polish included, since the time of the old cosmetics directive 76/768/EEC. The list of substances prohibited in EU cosmetics is Annex II of the cosmetics law.
DEP is not among the four phthalates restricted by REACH entry 51, and the assessments cited above, by the CIR, the FDA and the 2001 review, do not place it with DEHP or DBP. The word phthalate in two articles can refer to two substances assessed very differently.
The distinction has practical consequences. A rule restricting phthalates in toys or electronic equipment concerns plasticising phthalates in plastics, not solvents in perfume. To know which substances a rule applies to, one has to read the list of names and CAS numbers in the text itself.
Slogans and substance names
A label saying phthalate free answers a question it does not state. It does not say which substance was removed, nor which substance took its place. If DEP was removed, what replaced it may be another solvent with a safety profile of its own. The slogan speaks of absence; the substance name speaks of presence.
The ingredient list is where presence can be read, but it has limits. When DEP is added directly to a product, it has its own name in the ingredient list: Diethyl Phthalate. When it sits inside a fragrance composition, EU law allows the composition and its raw materials to be named together by the word parfum. The FDA likewise notes that in the United States fragrance may be listed simply as fragrance, so consumers cannot always spot phthalates from the label.
The words separated from parfum on an EU label are the fragrance allergens, as the essay The Names at the End of the Ingredient List explains. DEP is not on that list. Another substance often found in perfume in a role close to a fixative is: benzyl benzoate, softly balsamic, faintly floral, a quiet base note. It must be named above 10 ppm in leave-on products, and it has an IFRA restriction standard dating from 2020.
The most useful way to read is therefore not to hunt for a frightening word or a reassuring slogan. It is to find the substance name, then ask about dose, about route of exposure, and about the assessment already made for that exact substance. The essay An Ingredient List Read from the Top goes through that way of reading line by line.
Alcohol, carrier oils and other choices
The main solvent of perfume is ethanol. Perfumer's alcohol is high strength ethanol, usually denatured under each country's rules, with the denaturant chosen to interfere as little as possible with odour. Alcohol evaporates fast, lifting odorous molecules off the skin in the first minutes, then leaves.
Materials handed down from times before DEP also pass through alcohol. A tincture is the simplest extraction: the material is steeped in alcohol for weeks or months, filtered, and the solution kept as it is. Vanilla, tonka bean and benzoin are plant materials that distil poorly and are often prepared this way.
Dipropylene glycol, DPG for short, is another nearly odourless solvent, evaporating far more slowly than ethanol, often used to dilute thick materials or as a base for reed diffusers. Each solvent has its own properties and its own assessment record; no solvent is exempt from the question of dose and use.
Perfume oils take another path: no alcohol, the odorous molecules dissolved in a non-volatile carrier such as jojoba or fractionated coconut oil. The library's vegetable oils and butters page records the fatty acid make-up and shelf life of each. A carrier oil makes scent project closer to the skin and more slowly; it also brings its own questions about oxidation. Choosing a solvent is choosing how scent leaves the bottle, and it should be spoken of by substance name.
A scentless substance is still a substance.
It has a name, a CAS number, an assessment record.
A collective word has none of these.