How Does Dry Cleaning Work? Clothes Are Soaked in Solvent

Dry-cleaned clothes are washed in a liquid. About 1 gallon of perc solvent goes into the drum for every 2 pounds of clothing, and the load tumbles in it for 5 to 10 minutes, according to a 1995 review by the International Agency for Research on Cancer (IARC).

Cleaning with volatile liquids was known as “French cleaning” in Scotland and “chemical cleaning” in Germany, the IARC records, and such processes were eventually called dry cleaning “because they do not involve the use of water.” The perc wash it describes is not entirely water-free either: detergent and “a small amount of water” go into the tank with the solvent, because they “increase the solubility of dirt.”

How does dry cleaning work?

Dry cleaning washes clothes in a liquid solvent instead of water, most often perchloroethylene (perc). The load tumbles in solvent in a washer-like machine; the solvent is drained, spun out and evaporated with warm air, then recovered for reuse. Unlike water, the solvent does not make fibers swell, the change that can shrink or wrinkle fabric.

Water swells the fibers that solvent leaves alone

Water is a polar liquid that binds to polar groups in natural fibers, while most dry-cleaning solvents are non-polar. Cotton is about 90 percent cellulose. Its long chains are held side by side by hydrogen bonds, the same kind of bond that holds ice in its open, floating lattice.

Wool, a protein fiber, can absorb almost a third of its own weight in water. Heat and moisture also open the scales on its fibers, and agitation makes them latch onto each other, which shrinks the garment. Felt is made this way on purpose.

The IARC review explains the difference: “Aqueous solvents swell the hydrophilic textile fibres, so that the dimensions of the fibre change, which can cause wrinkles or shrinkage of the fabric. Nonaqueous dry cleaning solvents do not swell the fibres and can remove oily stains at low temperatures.”

The wash also runs cool: the IARC gives the best solvent temperature as 75 to 80 degrees Fahrenheit.

A drained load still holds gallons of solvent

Stained clothes are first “spotted” with chemicals. The IARC’s figures for the rest of the perc process come from a 1979 description of it.

Step	What happens	Perc in the load
Wash, 5 to 10 min	Clothes tumble as solvent cycles through filters	About 50 gallons per 100 pounds (1 gallon per 2 pounds)
Drain	Solvent runs out through a strainer that traps buttons, coins and pins	11 to 12 gallons left per 100 pounds
Spin, 3 to 5 min	The drum turns at 350 to 450 revolutions per minute	2 to 3 gallons left per 100 pounds
Dry, 10 to 25 min	Air at 120 to 150 F evaporates the rest	Condensed back to liquid

The filters are coated with diatomaceous earth and activated carbon to remove loose dyes and insoluble dirt, and most dry cleaners also distill the solvent for reuse. Afterward the clothes are pressed with steam.

Early dry cleaners washed clothes in gasoline and turpentine

The first solvent, the IARC says, was “camphene,” a 19th-century name for a lamp fuel distilled from turpentine. Benzene and petroleum liquids such as naphtha and gasoline followed. US dry cleaning dates to the 1800s, according to a 2021 review in Frontiers in Public Health, when people “washed fabrics in open tubs with solvents such as gasoline, kerosene, benzene, turpentine, and petroleum and then hung to dry.”

The main hazard, the IARC says, “was fire.” In the 1920s, W.J. Stoddard, president of the US National Institute of Drycleaning, introduced Stoddard solvent, a petroleum solvent that was “less inflammable and odour-free.”

Carbon tetrachloride, the first chlorinated solvent used in dry cleaning, came in because petroleum solvents were expensive, and it does not burn. By 1940 an estimated 20 thousand tonnes of it a year went into US dry cleaning, but it was dropped in the 1950s “because of its toxicity and corrosiveness.”

Perc, also nonflammable, took its place: its use “began to increase in the 1940s, and by the late 1950s it had virtually replaced carbon tetrachloride and trichloroethylene in commercial dry cleaning.” Petroleum solvents still led until perc became the US solvent of choice in 1962, a chronology by a coalition of state cleanup programs records.

The spilled-lamp origin story is unverified

The IARC opens its history with a hedge: dry cleaning “is believed to have originated in France in 1825.” It then relays an account from the French Federation of Dyeing and Cleaning, in which a servant in the Paris household of Jean-Baptiste Jolly “spilled the contents of a lamp on a soiled tablecloth. When the tablecloth dried, the spots had disappeared.”

The IARC guesses the lamp held camphene, but that name was coined in an 1838 US patent for a lamp burning distilled spirits of turpentine, 13 years after the supposed spill. Dry cleaners’ own websites retell the story with kerosene instead, dated variously to the 1840s or 1855. The spirits in that patent is the same word as in liquor, the alchemists’ name for a substance that rose as vapour in the heat.

Kerosene was barely known in the 1840s: Abraham Gesner said he first demonstrated it in 1846, and manufacture under his patents began in New York in 1854. None of these versions cites a record made at the time, so the spill remains an unverified story.

A document with a firm date points to New York. A list of patents that Secretary of State John Quincy Adams sent to the Speaker of the House, dated January 1, 1822, records one issued on March 3, 1821, to Thomas L. Jennings of New York for “Dry scouring clothes.”

Jennings was a free Black tailor. The list gives only “the dates, and general objects” of patents, so it does not say how his method worked.

Perc’s share has fallen since 1991

In 1991, perc was used in an estimated 28,121 US dry-cleaning plants, and 82 percent of commercial dry cleaners used it, by EPA figures the IARC cites. The 2021 review put the share using it as their main solvent at 60 to 65 percent, with most of the rest using a high-flashpoint hydrocarbon, a petroleum solvent built, like candle wax, from hydrogen and carbon. The EPA’s December 2024 rule estimated that 6,000 dry cleaners still use perc.

Other options include siloxane, liquid carbon dioxide and professional wet cleaning, in which “fabrics are cleaned with water and detergent in a computer-controlled washing machine.” A 2012 ranking by the Toxics Use Reduction Institute placed wet cleaning alone in its most-preferred group.

California’s air board started phasing out perc dry-cleaning machines in 2007, with a deadline of January 1, 2023. In December 2024 the EPA issued a final rule that set a 10-year phase-out of perc in dry cleaning and barred its use in newly acquired machines after 6 months. The agency based the rule on neurotoxicity, harm to the nervous system, from chronic exposure, and in 2025 it began a review to reconsider, and if appropriate revise, the rule.

The coat that comes back from the dry cleaner spent its wash soaked in solvent that will be filtered, distilled and used again on the next customer’s clothes. Strictly FYI.