For only the second time in its history, the American Red Cross has declared a “national blood supply crisis,” after donations fell to a four-year summer low.

The hotter summer months conventionally trigger blood shortages because people are more likely to injure themselves while spending time outdoors.

And this summer has been particularly extreme. According to the Red Cross, extreme heat, poor air quality, and widespread foodborne illnesses have compounded into blood donations dropping precipitously, causing supply levels to plummet to a historic low.

The news comes amidst record-breaking temperatures this summer, devastating heatwaves that have killed at least 25 people in the US. Public health officials are also battling an outbreak of an explosive diarrhea-causing parasite that’s has spread to 45 states.

As a result of plummeting donations, the Red Cross, which is the largest single provider of blood products, has “less than a one-day national supply of type O positive blood.” Type O positive is the most commonly transfused blood type since it can even be used when the patient’s blood type is unknown.

The Red Cross declared its first-ever national blood crisis in January 2022, triggered by a previous low in donor turnout due to ongoing COVID-19 surge disruptions.

“Every donation has the potential to help save lives, and we urgently need everyone who is eligible to make an appointment to give blood as soon as possible,” said Red Cross Biomedical Services president Chris Hrouda in a statement.

The risks of an extremely limited blood supply are considerable.

“There’s always the possibility, when the blood supply dips like it has, that patients won’t be able to get the blood products they need, when they need,” Red Cross spokesperson Matt Trotter told NPR affiliate KOSU.

By mid-July, the Red Cross was already ringing the alarm bells, warning that donations had fallen by about 25 percent in June.

To get back on track doesn’t require drastic action, either. The organization says that just “three more donors at each blood drive this summer can end this crisis and stabilize the blood supply.”

“One donation can help save multiple lives, so if you’ve got an hour you can spare, you can do a lot of good with it,” Trotter told KOSU. “Many people who think they are ineligible actually can donate blood.”

If you or a loved one wants to donate blood, this site run by the Red Cross can help find a blood drive nearby.

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