Dry cleaning solvent is any liquid chemical used to clean fabrics without water. The most common one, used by roughly 60 to 65 percent of dry cleaners in the United States, is perchloroethylene, a synthetic chlorinated compound widely known as “perc.” The remaining shops mostly use high-flashpoint hydrocarbon solvents, with a smaller number turning to silicone-based liquids or liquid carbon dioxide.
How Dry Cleaning Solvents Work
The key principle is polarity. Water is a polar molecule, which makes it excellent at dissolving salts and sugars but poor at pulling out oils, greases, and body oils embedded in fabric fibers. Dry cleaning solvents are non-polar, meaning they have a natural chemical affinity for fats and lipid-based stains. When clothing is submerged and agitated in these solvents, oily compounds dissolve directly into the liquid, much the way grease dissolves in cooking oil but not in water.
This non-polar action is also why dry cleaning is gentler on many delicate fabrics. Water causes natural fibers like wool and silk to swell, distort, and shrink. Solvents pass through the fibers without triggering that swelling, which preserves the garment’s shape and texture. That said, perc can damage certain materials like leather and suede, so the process isn’t universally safe for every fabric.
Perchloroethylene: The Dominant Solvent
Perc (chemical formula C₂Cl₄) is a colorless, dense liquid with a sharp, sweet odor. It became the industry standard beginning in the 1940s, replacing earlier and more hazardous solvents like gasoline, Stoddard solvent, and carbon tetrachloride. Its popularity comes down to performance: perc dissolves a wide range of stains effectively and evaporates cleanly from fabric without leaving residue.
Modern dry cleaning machines are “dry-to-dry” systems, meaning clothes go in dry and come out dry. The machine washes, extracts, and recovers the solvent in a closed loop. Older “transfer” machines required workers to move solvent-soaked clothing from a washer to a separate dryer, which released far more chemical vapor into the air. Those machines have been largely phased out.
Health and Environmental Concerns
Perc is classified by the International Agency for Research on Cancer as having limited evidence of causing bladder cancer in humans. California’s Air Resources Board goes further, listing it as a toxic air contaminant with no safe exposure level. Short-term exposure at high concentrations can cause dizziness, headaches, and confusion. Workers in older or poorly ventilated shops face the highest risk.
The environmental record is also significant. Decades of improper disposal have left a legacy of contaminated soil and groundwater across the country. When perc is released, whether through spills, leaking sewer lines, or waste dumped on the ground (a common practice before the mid-1980s), it sinks through soil and dissolves into groundwater. The contamination plume spreads in the direction of water flow, threatening private and public wells. Dry cleaning sites in urban areas have been a major source of groundwater contamination nationwide.
For consumers, the main concern is residual solvent on freshly cleaned garments. Perc can off-gas from clothing after you bring it home, releasing small amounts of vapor into your living space. Removing the plastic bag and airing out garments near an open window or in a well-ventilated area for a few hours reduces this exposure considerably.
Regulatory Phase-Outs
California has been the most aggressive jurisdiction in restricting perc. Starting in 2008, no new perc machines could be installed in the state. By 2010, perc machines in buildings that shared a wall with a residence had to be removed. Machines older than 15 years were retired on a rolling basis, and as of January 1, 2023, the use of perc for dry cleaning in California is completely banned. Other states and the EPA have pursued tighter regulations as well, though a full nationwide ban has not taken effect.
Alternative Solvents
The push away from perc has driven adoption of several alternatives, each with distinct trade-offs.
- High-flashpoint hydrocarbons (such as DF-2000) are synthetic petroleum-based solvents containing chains of 11 to 15 carbon atoms. They are nearly odorless and considered safer than perc for workers, though they can irritate the eyes, nose, and lungs at high concentrations and cause skin dryness with repeated contact. They clean effectively but work more slowly than perc and require longer drying cycles because they evaporate at higher temperatures. Reviews by California’s environmental health agency have found them safer than older petroleum solvents that contained benzene.
- Silicone-based solvents (decamethylcyclopentasiloxane, or D5) are odorless, colorless liquids already common in consumer products like lotions and deodorants. They are gentle on fabrics, produce less environmental contamination than perc, and break down relatively quickly when released into the atmosphere. Their cleaning power on heavy grease stains is somewhat lower than perc’s.
- Liquid carbon dioxide uses pressurized CO₂ in a specialized machine. Because liquid CO₂ has less raw dissolving power than perc, the process relies on mechanical agitation and added surfactants (cleaning boosters) to compensate. It leaves no chemical residue on clothing and produces no toxic waste, but the equipment is expensive and requires higher-pressure chambers, which has limited adoption.
- Professional wet cleaning uses water combined with specialized detergents, controlled temperatures, and precise agitation in computer-managed machines. It avoids solvents entirely. While effective for many garments, it requires more skill to prevent shrinkage on sensitive fabrics.
What the Labels on Your Clothes Mean
When a care label says “dry clean only,” it means the manufacturer tested the garment and determined that water-based washing poses a risk of shrinkage, color bleeding, or structural damage. It does not specify which solvent a cleaner should use. Some labels include a circle with a letter inside: “P” means any solvent except trichloroethylene, “F” means petroleum-based solvents only, and “W” indicates professional wet cleaning is appropriate. If you want to avoid perc specifically, asking your cleaner which solvent they use is the simplest approach. Many shops now advertise their alternative methods as a selling point.