WD-40 is mildly toxic. It’s made almost entirely from petroleum-based hydrocarbons, which can irritate your skin, eyes, and lungs on contact. A brief spray on a squeaky hinge won’t hurt you, but swallowing it, soaking your skin in it, or breathing heavy fumes in a closed space can cause real harm. The biggest risk is inhaling the mist or accidentally aspirating the liquid into your lungs.
What’s Actually in WD-40
The exact formula is a trade secret, but the Safety Data Sheet breaks down the broad categories. About 45 to 50 percent is a light petroleum distillate (the solvent that penetrates and loosens things). Up to 35 percent is petroleum base oil (the lubricant that stays behind). Another 10 to 25 percent is an additional hydrocarbon solvent, and 2 to 3 percent is carbon dioxide, which serves as the aerosol propellant.
In plain terms, WD-40 is mostly refined petroleum products similar to mineral spirits or light machine oil. It does not contain benzene, and none of its listed ingredients are classified as known human carcinogens. That said, petroleum distillates are not harmless, particularly when inhaled or swallowed.
Inhalation Is the Biggest Concern
Spraying WD-40 releases a fine mist of petroleum solvents. In a well-ventilated garage, brief exposure causes little more than a strong smell. In a small, enclosed space like a closet, bathroom, or car interior, the vapor concentration can climb quickly. Short-term symptoms of overexposure include dizziness, headache, nausea, and irritation of the nose and throat.
The more serious risk is chemical pneumonitis, an inflammation of the lungs caused by inhaling chemical fumes or accidentally breathing liquid droplets into the airways. Acute cases cause a burning sensation in the chest, wet-sounding breathing, coughing, and the feeling of not being able to get enough air. Chronic low-level exposure over time can stiffen lung tissue and progressively reduce your ability to breathe. Untreated, severe chemical pneumonitis can lead to respiratory failure. This is the same reason the label warns against intentional inhalation, which concentrates the vapors far beyond what normal use produces.
Skin and Eye Contact
Getting WD-40 on your skin occasionally is unlikely to cause lasting harm. The petroleum solvents strip natural oils from your skin, so prolonged or repeated contact can lead to dryness, redness, and irritation similar to what you’d get from handling mineral spirits without gloves. Washing the area with soap and water is usually sufficient.
Eye exposure is more urgent. The solvents cause stinging, redness, and tearing. If WD-40 gets in your eye, flush it immediately with clean, lukewarm tap water for at least 20 minutes. Remove contact lenses first. Hold your eyelid open and let a gentle stream of water run across the eye, either from a faucet, a shower aimed at your forehead, or a workplace eye-rinse station. Don’t rub the eye, and don’t add eye drops unless emergency personnel tell you to. If irritation persists after flushing, seek medical attention and bring the can with you.
What Happens if You Swallow It
Swallowing WD-40 is uncommon in adults but does happen, particularly with young children who get hold of the straw or tip. Petroleum distillates irritate the lining of the mouth, throat, and stomach. Nausea, vomiting, and diarrhea are the most likely symptoms. The bigger danger is aspiration: if the liquid is vomited back up and inhaled into the lungs, it can trigger chemical pneumonitis even from a small amount. For this reason, you should not try to induce vomiting after ingestion. Contact Poison Control (1-800-222-1222 in the U.S.) for guidance.
Risks for Dogs and Cats
Pets that lick a surface freshly sprayed with WD-40, or that walk through it and groom their paws, are getting a small dose of petroleum solvents. A small taste is unlikely to cause serious poisoning. The most common reaction is gastrointestinal upset: vomiting, drooling, or diarrhea. The greater concern, as with humans, is the lungs. If a pet inhales the spray or aspirates any liquid, it can develop breathing difficulties and a cough. Oil-based solvents are particularly problematic because they spread easily across lung tissue.
If your pet has significant exposure, move it to fresh air and contact your veterinarian or the ASPCA Animal Poison Control Center (888-426-4435). Keep the product container handy so you can report the ingredients.
How to Use It Safely
Normal, occasional use of WD-40 carries low risk as long as you follow a few practical rules:
- Ventilation matters most. Spray in open or well-ventilated areas. If you’re working indoors, open a window or turn on a fan.
- Keep exposure brief. Spray, do the job, and move on. Don’t linger in a cloud of mist.
- Wear gloves for extended projects. If you’re degreasing a chain or soaking a rusted bolt, disposable nitrile gloves prevent the solvent from stripping oils from your skin.
- Store it away from children and pets. The straw attachment makes it easy for a curious child to spray directly into their mouth or eyes.
- Never heat the can or spray near open flame. The petroleum solvents are flammable, and the pressurized can poses an explosion risk.
WD-40 is not acutely dangerous with ordinary use. It falls in the category of household chemicals that are safe when handled with basic common sense but can cause real harm when misused, overexposed to, or swallowed. The petroleum solvents are the source of essentially all its toxicity, and ventilation is your single best protection against them.