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If you read the back of a motor oil container, you will likely find stern warnings indicating that drinking motor oil could be fatal. This is true. However, why it is true has more to do with the physical characteristics of motor oil than its chemical makeup.
Motor oil belongs to a large class of compounds called hydrocarbons. In their simplest form, hydrocarbons are combinations of carbon and hydrogen atoms. There are many varieties of hydrocarbons, but all hydrocarbons tend to feel oily to the touch when in their liquid state. When these oily substances are swallowed, the worry is that they can slip into the airway or be inhaled later during the process of vomiting. This is called aspiration, which can be very irritating and lead to infection. The airway is right next to the food pipe, and the close proximity is the reason aspiration happens. The ease of which a substance can flow is the characteristic known as viscosity. Low viscosity (thinner) hydrocarbons are more likely to be aspirated than high viscosity (thicker) hydrocarbons.
When a small amount of motor oil is swallowed and goes down the food pipe into the stomach, the only symptom that is expected is a laxative effect (loose stools or diarrhea). This type of exposure can be safely watched at home. However, if motor oil is aspirated or suspected of being aspirated, the person should be taken to an ER for evaluation. A product might have been aspirated if the person coughs (as if something has gone down the airway) or vomits. In the ER, the patient will be evaluated and typically have a chest x-ray to look for any inflammation in the lungs.
Used motor oil has contaminants that are not present in new motor oil. When a car is running, motor oil is exposed to high heat, which creates new chemicals that can be more toxic than the oil itself. Additionally, while circulating through the car machinery, motor oil collects heavy metal contaminants. Always recycle or properly dispose of motor oil to avoid polluting the environment with these contaminants. Used motor oil also has the risk of aspiration. The addition of contaminants, although toxic, would not change the management of the aspiration. A one-time unintentional exposure to used motor oil without aspiration is not expected to cause any additional toxicity.
Like all hydrocarbons, motor oil can cause defatting of the skin. Defatting is the dissolving of oils and fats in the skin and may cause pain, irritation, or swelling of the skin after direct contact. If you get motor oil on your skin, wash well with soap and water as soon as possible. A mild lotion can be used to help with the dryness. Severe cases of defatting may require surgical treatment.
If you think someone has been exposed to motor oil, immediately call Poison Control at 1-800-222-1222 or check the webPOISONCONTROL®online tool for help. Whether you call or log on, expert assistance is available 24 hours a day.
Pela Soto, PharmD, BSHS, BS
Certified Specialist in Poison Information