WASHINGTON (AP) — Health officials are urging Americans to take precautions as extreme heat blankets much of the Midwest and Eastern United States ahead of the Independence Day weekend, warning that prolonged exposure can quickly become life-threatening.

Experts recommend limiting outdoor activity during the hottest hours of the day, typically between late morning and early evening, and staying in air-conditioned buildings whenever possible. Those who must be outside should seek shade frequently, wear lightweight, loose-fitting clothing and a wide-brimmed hat, and drink water regularly without waiting until they feel thirsty.

Older adults, infants and young children, pregnant women, outdoor workers, and people with chronic medical conditions face the highest risk of heat-related illness. Officials also advise checking on elderly neighbors, relatives and anyone without access to air conditioning during periods of extreme heat.

Doctors warn that several commonly prescribed medications — including some for high blood pressure, heart disease, allergies, ADHD and mental health conditions — can make it harder for the body to regulate temperature or increase the risk of dehydration. Patients should continue taking prescribed medications but consult their healthcare provider about additional precautions during heat waves.

People should learn to recognize the warning signs of heat exhaustion, including dizziness, heavy sweating, nausea, muscle cramps, headache and weakness. Anyone showing signs of heat stroke — such as confusion, slurred speech, seizures, unconsciousness or a body temperature above 103 degrees — should be moved to a cool location immediately while someone calls 911. Rapid cooling with water, ice packs or air conditioning can be lifesaving while waiting for emergency responders.

Health officials also recommend avoiding strenuous exercise during peak heat, never leaving children or pets in parked vehicles, and using fans only when temperatures are not dangerously high, as fans alone may not prevent heat-related illness during extreme heat.