Dallas County has registered two heat deaths so far this year, according to the health department.

There will be more.

The National Weather Service says the next seven days are all expected to have temperatures above 100 degrees. Humid air is sending the heat index higher, with readings touching 105 Thursday and Friday and “cooling” to 102 this weekend.

That means heat-related dangers are once again a major threat. And experts — meteorologists and doctors alike — say temperatures don’t have to zoom past the century mark to cause problems associated with heat-related illnesses such as heat cramps, heat exhaustion, heatstroke or even death.

Texas led the nation in heat-related deaths in 2011 with 46. The beginning of August is “the hottest part of the year,” said David Finfrock, chief meteorologist for KXAS-TV (Channel 5). Although Dallas isn’t likely to have another record run of days 100 degrees or hotter this year, it doesn’t have to be that hot to be dangerous.

“When temperatures outside approach your own body temperature — around 98 degrees — that’s when you get into trouble,” said Dr. Paul Pepe, city of Dallas director of medical emergency services.

The experts say humidity plays a big role in causing trouble when it comes to the heat. Skin acts as a cooling device for the body, much as a radiator does for a car. When a person perspires, the sweat evaporates, which cools the body.

“When it’s humid, it’s difficult for perspiration to evaporate,” Finfrock said. “Since the body is not cooling itself, you feel the heat more.”

To give people a better idea of how hot they really feel, meteorologists developed the heat index, a weather reading that takes humidity into consideration. As they do with wind chill, they advise audiences to take precautions when there is a significant difference in temperature and heat index.

“Anything above 105 is going to have a significant effect on the human body,” Finfrock said. “The more time outside, the harder it is on the body. Core body temperatures will continue to rise. It’s like having a fever.”

This increase in body temperature happens much quicker in people over age 65 and young children, whose temperatures rise at nearly five times the pace of healthy younger adults, experts say.

“Though they are resilient, the simple fact is that their small bodies don’t tolerate the same types of exposure that healthy adults do,” said Jason Evans, public information officer for Dallas Fire-Rescue.

The most common heat-related illnesses are heat cramps, heat exhaustion and heatstroke.

“Each one gets progressively worse,” Evans said. “One can lead to the other.”

A heat cramp can happen while exercising and usually affects the legs, back, abdomen or shoulders.

“If you’ve ever had any type of muscle cramp, you know what a heat cramp feels like,” Evans said.

Heat exhaustion involves dehydration and a shortage of salt in the body caused by sweating too much. Symptoms include dizziness, fatigue, headaches and nausea. Victims tend to have dark-colored urine, a sign of dehydration, and are cold to the touch because of profuse sweating.

Heatstroke is the most severe of the three and can occur as a result of failure to address heat exhaustion. When body temperatures begin to exceed 104 degrees, cooling mechanisms start to shut down and cells begin to die. Though there is no specific timetable, it can quickly turn fatal, said Jan Null, a meteorologist at San Francisco State University.

“Its like throwing a circuit breaker on your body,” Null said.

According to Pepe, it is difficult to track statistics on heat-related illnesses because they often coincide with other ailments.

“A lot of people come in with underlying chronic illnesses that are probably activated by the heat,” he said.

But Evans said many of the calls Dallas Fire-Rescue responds to involve healthy children who have been left alone in a car.

And temperatures don’t even have to be excessive to be a threat to youngsters. A 5-month-old El Paso girl died in May of heat-related causes after being left alone in her car. The outside temperature was 78 degrees.

According to Null, if it is 100 degrees outside, temperatures in a vehicle can reach more than 120 in just 10 minutes. After an hour, temperatures rise about 43 degrees, making it well over 140 in the car.

In the El Paso girl’s case, the temperature inside her vehicle had escalated well above 110 degrees within one hour.

“It’s not survivable for very long,” Null said, “especially for an infant or a child.”

IN THE KNOW

How to beat the heat

Drink plenty of fluids, both before and after participating in outdoor activities. “You should drink enough fluid that you have to go to the bathroom all the time,” says Dr. Paul Pepe, city of Dallas director of medical emergency services.

Avoid drinks with high amounts of sugar and caffeine, including sports and energy drinks if not consumed during exercise. Pepe also warned against consuming alcohol: “It impairs your ability to know you’re getting into trouble and dehydrates you further. A nice cold beer sounds good, but it just makes things worse.”

BY THE NUMBERS

Sizzling stretch

2

Deaths in Dallas County this year from heat-related illnesses

6

Deaths in Texas in 2011 from heat-related illnesses. North Texas had a record 71 days of 100-plus temperatures that year.

7

Days forecast to have temperatures above 100 degrees starting Wednesday

105

Heat index temperature forecast for Thursday