The surface of Mars is rich with a chemical called perchlorate.

Perchlorate, which can form different salts, is a key reason why liquid water sometimes flows on the planet despite the atmospheric pressure. And it can be used as a major ingredient in rocket fuel. It can even be broken down and used as a source of electricity and oxygen for human explorers.

But it has also been linked to harmful health effects, such as hypothyroidism and a form of anemia.

The chemical was identified by NASA’s Phoenix lander in 2009 and since then, scientists found out that it is everywhere on the Red Planet — it’s 10,000 times more abundant in Martian dirt than it is in Earth’s sands and soils, Phys.org reports.

The discovery helped scientists figure out how liquid water could exist on Mars, affecting the planet’s surface.

Because of the thin Martian atmosphere, pure water can only exist as ice or vapor on the planet. But dissolved salts can change this chemistry, occasionally allowing liquid water to manifest as lakes or streams, Discover reports.

“Perchlorate could hold the key to understanding underground water, and in turn microorganisms that lend insight into space biology. In addition, it could help determine the right landing sites and positions of human colonies, and ‘changing’ Mars’ design to resemble Earth,” Discover writes.

But the existence of perchlorate is a double edged sword of sorts. For one, any liquid water formed from perchlorate would be especially briny and incapable of sustaining microorganisms. And it would be poisonous to drink.

The chemical has been associated with hypothyroidism and fatal blood cell deficiencies, Discover reports.

“This means that we’ll have to take extreme precaution to remove perchlorate from Mars water and dirt, or from any crops that we grow in it,” Discover writes. “Dust will have to be kept from contaminating air circulating through life support systems. Future explorers and colonists will have to do all of this, not only as they capture the perchlorate in order to reap its benefits, but also as they confront space radiation, physical deconditioning from low gravity, and other potential Martian threats to human health.”