Is WD-40 Toxic?

What Is WD-40 Multi-Use Product?

WD-40 Multi-Use Product is the original blue-and-yellow aerosol can found in almost every garage. People reach for it to quiet a squeaky hinge, loosen a stuck bolt, push water out of an electrical connector, and wipe off grime. It sprays on as a light oily film, then the thin carrier flashes off and leaves a protective residue behind.

WD-40 works best as a water displacer and short-term penetrant rather than a long-lasting lubricant, but that is a performance question, not a safety one. If you are shopping the broader lubricants and chemicals category, it covers the related sprays and greases.

What the Safety Data Sheet Says

These verdicts come from the hazard codes and GHS classifications in the manufacturer's Safety Data Sheet, not from CarCareTruth's opinion. The single most important thing to understand about WD-40 is that its scary-looking label is driven by how it burns and behaves as a pressurized spray, not by it being a poison.

GHS Hazard Classification

The label carries a DANGER signal word, which is the higher of the two GHS alert levels, along with the flame, gas-cylinder, and health-hazard symbols. The SDS lists four hazard codes (Source: WD-40 Company SDS, Section 2):

• H222 (extremely flammable aerosol): the spray and its vapor catch fire easily near any flame or spark.
• H229 (pressurized container that may burst if heated): the can itself can rupture if it gets hot.
• H280 (contains gas under pressure and may explode if heated): the propellant holds pressure that a fire or heat can turn into an explosion.
• H304 (can be fatal if swallowed and it enters the airways): if the light liquid slips into the lungs after swallowing, it can cause serious lung injury.

Three of those four are physical hazards. They describe fire and pressure, not what the chemical does to your body once it is inside. Only H304 is a health-hazard code, and it is specifically about the swallowing-into-the-lungs route. The SDS does not carry a DANGER warning because WD-40 is a poison. It carries one because it is flammable, pressurized, and an aspiration risk.

Key Ingredients

WD-40 is mostly petroleum chemistry. The main ingredient is a light aliphatic hydrocarbon carrier, a thin solvent that spreads the product and displaces water, then largely evaporates. A petroleum base oil is the heavier, non-volatile fraction that stays behind as the protective film. The propellant is carbon dioxide, which pressurizes the can and is not part of the working liquid. The exact percentages are a trade secret, and the SDS discloses a small share of non-hazardous ingredients as a proprietary mixture.

What Sections 8 and 11 Say About Exposure

The toxicology section is the part that clears up the confusion. Section 11 reports an oral toxicity above 5,000 milligrams per kilogram and a dermal toxicity above 2,000 milligrams per kilogram, and states the product is not classified as toxic by established criteria for swallowing, skin, or breathing. In plain terms, the manufacturer's own data does not place it in an acute-poison category.

Section 8 asks for adequate ventilation and notes that no respiratory protection is needed for normal use when the air is moving. It lists eye protection and gloves as sensible for heavy or overhead spraying, driven by the mist and by prolonged skin contact, not by a corrosive or sensitizing classification the product does not carry.

The Main Risk Pathways for Car Owners

For someone using WD-40 in a home garage, the hazards line up in a specific order. Fire comes first. It is an extremely flammable aerosol (H222) and a gas under pressure (H229, H280), so a pilot light, a water heater, a lit cigarette, a grinder spark, or a hot exhaust manifold near the spray is a genuine fire risk. This is the pathway most worth guarding against, and it is a physical hazard rather than a toxicity one.

Inhalation is second and situational. The product is not classified as toxic to breathe, but the aerosol form matters. Fine mist reaches deep into the lungs, and heavy spraying in a closed garage lets the petroleum vapor build up enough to cause a headache or dizziness. The SDS answer is ventilation. Working outdoors or with the doors open keeps the exposure low.

Pets and kids fold into the swallowing risk. WD-40 is not classified as acutely toxic to swallow, but it is an aspiration hazard (H304), so a curious dog or child who licks it and then coughs can draw the liquid into the lungs. If a person swallows any, do not induce vomiting, because bringing it back up is exactly how it reaches the lungs. Rinse the mouth and call Poison Control at 1-800-222-1222. If a pet swallows any, call your vet or the ASPCA Animal Poison Control Center at 888-426-4435.

What the SDS Does NOT Flag

A few common fears do not show up in the hazard data for this product. WD-40 carries no acute inhalation-toxicity code (no H330, H331, or H332) and is not a respiratory sensitizer (no H334), so respiratory protection for normal use is not driven by the SDS. It carries no acute oral or dermal toxicity code (no H301, H302, H311, or H312), no corrosive or skin-irritation code (no H314 or H315), and no cancer or reproductive-hazard code (no H350, H351, H360, or H361). Section 15 states the product does not contain chemicals regulated under California Proposition 65. Absence of a code means the manufacturer did not classify it that way; it does not by itself prove an ingredient is inert.

Aerosols and Aspiration: Where the DANGER Word Really Comes From

WD-40 is a good example of why a DANGER label does not always mean poison. The word is earned two ways here, and neither is systemic toxicity. The first is the aerosol itself. A pressurized can of light petroleum liquid is extremely flammable (H222) and holds gas under pressure (H229, H280), so it can ignite or burst. Those are fire and explosion risks you manage by keeping the can away from heat, flame, and sparks, not by wearing a mask.

The second is aspiration (H304). This is not about breathing the vapor. It means that if the thin hydrocarbon liquid is swallowed and then enters the airways, usually during vomiting or choking, it can spread across the lungs and cause a chemical pneumonia. Light petroleum distillates flow easily into lung tissue, which is why even a small swallowed amount can be a problem and why the first-aid rule is to never make someone throw up. Take the aspiration hazard seriously and take the DANGER word literally as a fire and lung warning, but do not read it as a sign that WD-40 is an acute poison, because the SDS toxicology data says it is not.

Safer Choices and Product Context

If you want the SDS-sourced detail for the specific can most of the country buys, see our full review of the WD-40 Multi-Use Product, which breaks down the DANGER label, the PPE the SDS lists, and how it scores on the CarCareTruth health scale. Its health picture is shaped mainly by the aspiration hazard and its high VOC content, not by any acute-poison classification, so the honest read is a flammable, aspiration-risk aerosol rather than a toxic one.

Sources and SDS Reference

• WD-40 Multi-Use Product SDS (WD-40 Company), revised 2014-07-20, Sections 2, 3, 8, 11, 15: SDS PDF (DANGER, H222/H229/H280/H304, petroleum distillates with a carbon dioxide propellant, not classified as acutely toxic in Section 11). This SDS revision is older than 12 months, so this assessment reflects the 2014-07-20 revision; verify against the current manufacturer SDS if the formula has changed.
• PubChem CID 280 for the carbon dioxide propellant identity.
• CarCareTruth ingredient and hazard-code pages, and the SDS database for looking up a product's sheet.