The St. Louis region is under an excessive heat warning through Thursday and public health officials are warning people to remain on guard against heat-related illnesses.

The St. Louis Coroner's Office is looking into one possible heat-related death from last week, but no other information was available Monday night.

The combination of high temperatures and humidity levels are expected to raise the heat index to 110 degrees or higher in the upcoming days. Monday's high temperature was 97.

The excessive heat advisory will be in effect through 8 p.m. Thursday, said Butch Dye of the National Weather Service in Weldon Spring.

St. Louis' interim health director, Pamela Walker, urged people to check on elderly family members and neighbors, to bring their pets indoors, and to limit outdoor activities to the morning and evening hours.

"Many heat-related illnesses can be prevented by taking the appropriate precautions," Walker said in a statement.

Hot, stagnant air also put a strain on local air quality.

The St. Louis Regional Clean Air Partnership put out a "yellow" air quality forecast for today after an "orange" forecast on Monday. During orange days, people with respiratory disease — including asthma — should limit prolonged outdoor activity.

During yellow days, those who are considered "very sensitive" to air pollutants should limit prolonged activity outside.

"Children, elderly, people who work outdoors, they need to be careful — even on a yellow day," said Susannah Fuchs of the American Lung Association of the Plains-Gulf Region.