We’ve heard all about how awful road salt can be: It’s corrosive and will eat away your car if you let it cling too long. But now there’s a new and even worse chemical being applied to roads in winter. It’s called brine, and it’s your car’s worst nightmare.

The Washington Post just did a big story about why brine is being used now to keep roads clear (it’s a liquid and doesn’t bounce off like rock salt) and why those same reasons are part of why it’s so bad for vehicles. Salt is the common name for sodium chloride (remember chemistry class?). Brine isn’t that. Brine is magnesium chloride plus sodium chloride, plus water to make it stick and not bounce. Magnesium chloride is even more corrosive than salt, and unlike the little pebbles that may or may not cake to your car, brine sticks and stays.

But that’s not the worst bit. We know that rusting doesn’t happen in a dry environment; you need wetness for that. That means humidity, a bit of warmth. Salt corrodes when the humidity is up around 70, according to The Washington Post. But brine? Only 20-30 percent. From the Post:

So, avoid warmer garages. On a bitter cold morning a few days ago, the temperature two levels down in The Washington Post’s underground garage was 44 degrees. That temperature can support a relative humidity above 30 percent. If your car is coated with magnesium chloride, it will turn wet at that temperature: corrosion city. Chilly but not frigid in your garage at home? Same issue.

“Inside that garage is a 100 percent time of wetness and a very corrosive situation,” said Baboian, who has written two books on automotive corrosion. “Sometimes the corrosion rate can be 100 to 1,000 times faster in the higher humidity and the higher temperature.”

Brine isn’t going away. More municipalities are switching away from road salt because brine works better, and it’s less expensive. For city officials and taxpayers, brine is a no-brainer. But for car owners, it’s awful. It may mean less icy-road accidents, which saves everybody money and hassle (not to mention safety). But it’s also going to mean motorists will need to invest in more frequent car washes, as well as undercarriage washes.

It’s the only way, folks.