Maryland has recorded 29 heat-related deaths so far this summer — surpassing the total number of people who died from heat illness in 2024, which had already been a deadlier-than-usual summer.

With four new heat-related deaths reported Wednesday by the Maryland Department of Health, heat has claimed more lives in Maryland this summer than in any other year in over a decade.

This summer surpasses 2018, when 28 people died from heat, but trails 2012, when state health officials attributed 46 deaths to heat.

That was the year a derecho storm ripped through the region in late June, knocking out power for millions just as a heat wave took hold. In areas of Maryland without power in the wake of that storm, heat killed 17 people, according to a National Weather Service report from the time.

This summer, the overwhelming majority of people who have died from heat have been adults older than 65, according to the latest available state data.

To Dr. Clifford Mitchell, director of the Maryland Department of Health’s Environmental Health Bureau, this shows the importance of checking in with friends, family and neighbors — especially older residents who may have limited access to air conditioning.

For the most part, said Mitchell, “heat-related deaths are 100% preventable. Especially these deaths.”

The state health department releases weekly surveillance reports of heat-related illness and deaths between May and September. In addition to surpassing the number of heat-related deaths for all of 2024, this summer already had seen hundreds more hospitalized from heat than any other summer in the last five years.

Nearly 1,500 people have gone to emergency rooms or urgent care centers for heat-related illness as of Aug. 9, the latest date covered in the health department report. Over 1,000 people have called for emergency medical services.

High heat is the deadliest form of extreme weather, killing tens of thousands of people around the globe every year. Experts predict more people will die or get sick because of the heat as human-cause climate change intensifies.

Still, this summer has proven deadly even without extraordinary heat.

Baltimore has experienced 25 days with temperatures 90 degrees or hotter since May 1, according to National Weather Service data, well below the 41 days when temperatures climbed that high by this point last year.

A possible culprit for the rise in deaths is the humidity, which compounds heat’s toll on the body.

It’s been an especially muggy summer in the mid-Atlantic, with much of the region setting records for days with oppressive humidity. According to an Associated Press report this week, Baltimore has seen at least 24 days with dew points of 75 degrees or higher — an indicator of near-tropical humidity.

That makes this the most humid summer Baltimore has seen in more than 30 years, said Brian LaSorsa, science and operations officer in the Baltimore-Washington division of the National Weather Service.

So even though this summer hasn’t been a standout for heat — it’s not even in the top 50 years dating back to 1871 when it comes to days topping 90 degrees — LaSorsa said many factors could be driving this year’s heat deaths, including access to air conditioning, cloud cover and oppressive humidity.

Extreme heat kills by disrupting the body’s ability to regulate itself. A person typically begins by feeling heat cramps, which are the first symptom of heat illness and can lead to heat exhaustion and heat stroke. Mitchell noted that the combination of extreme temperatures with persistent humidity is even harder on the body.

Heat exhaustion symptoms include heavy sweating; cool, clammy skin; weakness and tiredness; dizziness; and nausea. Heat exhaustion can transition into heat stroke, which is a medical emergency.

Heat stroke symptoms include confusion and slurred speech, throbbing headaches and a body temperature above 103 degrees. A person experiencing heat stroke needs medical attention immediately.

After a relatively mild start to August last week, high temperatures returned to the Baltimore region Sunday. The high forecast for Baltimore on Wednesday was 92 degrees.