Windshield Washer Fluid: A Winter Hazard

What is windshield washer fluid?

Automotive windshield washer fluid is a solution that will not only help clean a windshield, but also prevent windshield washer tanks and hoses from freezing in the winter. When used according to the product instructions, windshield washer fluid can lower the freezing point of washer tank contents by 20–35° F. The solution can also help melt ice and snow on a windshield.

Is windshield washer fluid poisonous?

Windshield washer fluid that is poured directly into the washer tank typically contains 30–50% methanol, while products labeled “concentrate” can contain as much as 90–100% methanol. These products are diluted with water before use. Methanol is a highly toxic alcohol. Very small amounts are poisonous to children, adults, and pets. 

What are the symptoms of windshield washer fluid poisoning?

Drinking windshield washer fluid often causes stomach upset and vomiting at first. The most serious symptoms of methanol poisoning don't happen for a while. Someone could swallow a fatal amount and feel fine for a few hours. Later, the person who swallowed it might appear dizzy, sleepy, confused, or even drunk. Meanwhile, their body is metabolizing methanol into formaldehyde and formic acid, which are responsible for the delayed but severe results of methanol poisoning. 

The most important delayed effects of windshield washer fluid poisoning are making the blood more acidic, brain damage, and impaired vision. Eye symptoms range from blurred vision to complete blindness. Without prompt treatment in an emergency room, a person with methanol poisoning could suffer permanent blindness or even coma and death.

Are there treatments for methanol poisoning?

Methanol is absorbed from the gastrointestinal tract very rapidly, so there is no practical way to prevent absorption. Hemodialysis can be used to remove some methanol and its toxic by-products from the bloodstream. Other treatments focus on slowing the metabolism of methanol into formaldehyde and formic acid. This gives the body a chance to clear methanol before it gets transformed into its toxic byproducts through excretion into the urine or by hemodialysis. 

Ironically, the primary treatment for methanol poisoning for many years was considered to be ethanol, which can itself be toxic in large quantities. Ethanol is metabolized by the same enzyme system as methanol, but its by-products are not as toxic as methanol’s. High concentrations of ethanol acted to tie up the enzymes and slow the metabolism of methanol. Currently, the best treatment for methanol poisoning is fomepizole. This drug slows the metabolism of methanol without the added complication of ethanol intoxication.

What to do if you think someone drank windshield wiper fluid.

If you suspect that someone has tasted or swallowed windshield wiper fluid, immediately use the webPOISONCONTROL online tool or call Poison Control at 1-800-222-1222. Both will tell you exactly what to do and are available 24 hours a day.

Robert Porter, BS, MPH, PharmD
Certified Specialist in Poison Information

Revised William G. Troutman, PharmD
Professor of Pharmacy Emeritus

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