Acetone is an extremely flammable liquid that is combustible at room temperature. Flames can travel through acetone vapor in the air to the liquid itself. Vapor can accumulate in a confined space, which may increase the risk of ignition. Even when diluted with water, an acetone solution can still be flammable.
Direct skin contact with acetone is usually not very severe and is either not at all irritating or mildly irritating. In a study cited by the Canadian Centre for Occupational Health and Safety, volunteers exposed to acetone for 90 minutes only experienced mild swelling. There is very little danger of absorbing acetone into the body through contact with unbroken skin.
While acetone is not very irritating to skin, it is extremely irritating to eyes. Studies cited by CCOHS have shown corneal damage due to contact with liquid acetone, though this damage was completely healed within 48 hours. In at least one case, permanent clouding of the cornea was reported, however, this was due to prolonged exposure to acetone. Acetone vapors can be irritating, though they usually do not cause damage.
The effects of consuming acetone are not extremely severe; if swallowed it will usually cause the person to feel drunk. Ingesting acetone can be dangerous if it is breathed directly into the lungs during ingestion or vomiting it can cause life-threatening lung injury.
Acetone has not been shown to cause cancer. Long term exposure to skin can produce dermatitis-dry, irritated skin. Research cited by CCOHS has not shown any extreme long term effects to exposure to acetone vapors. However, according to CCOHS, there are not many conclusive studies regarding the long term effects of exposure to acetone.