High humidity levels and 90-degree heat are expected to make a sweltering combination today and Saturday, with the possibility of making temperatures feel like more than 100 degrees.

The Allegheny County Health Department issued a warning Thursday saying that the "extreme" heat and humidity could pose a health risk for senior citizens, infants, children as old as 4, people with heart and respiratory problems, people who work outside and people who are overweight.

These conditions are dangerous because high humidity prevents sweat from evaporating, a process that cools the body, said Pat Herald, a meteorologist at the National Weather Service. The humidity and heat should diminish by Sunday, he said.

There have been four days this month with temperatures above 90 degrees -- July 5 to 8 -- that have helped make this summer 2 to 4 degrees hotter than average, Mr. Herald added.

The health department suggests people:

• Stay cool indoors. Air-conditioning is best, but a cool bath and shower can also work. Senior centers, malls and theaters usually have air-conditioning.

• Drink at least eight glasses of water per day. Alcoholic and caffeinated drinks should be avoided because they are dehydrating, as should hot foods and heavy meals, which make the body hotter.

• Wear lightweight, light-colored and loose clothing.

• Avoid strenuous activity.

• Never leave a child or pet in a vehicle alone.

• Check with senior citizens and people with medical conditions who do not have air-conditioning and might be less able to take care of themselves.

There is also a chance for showers and storms over the weekend, most likely starting Saturday night, Mr. Herald said.

The senior centers in the county will have normal hours, usually closing at 4 or 5 p.m. The Homewood center at 7321 Frankstown Ave. and the South Side center at 12th and Bingham streets will be open until 7 p.m., with refreshments and activities for people over 60.

The county has delivered emergency kits to 800 people who live alone and have medical conditions, said Mildred Morrison, administrator of the county's Area Agency on Aging. The agency will also be calling high-risk seniors to ensure they are keeping cool, she added.

Warning signs for heat exhaustion include heavy sweating, paleness, fainting, fatigue, dizziness and vomiting. If the symptoms are severe and the person has health problems, medical attention should be sought immediately. Otherwise, help the person cool off and seek medical assistance if symptoms worsen or last for more than an hour.

Warning signs for heat stroke, which is more serious and can be life-threatening, include red, hot and dry skin; unconsciousness; a rapid pulse; throbbing headache; and dizziness. Medical assistance should be sought immediately. Bystanders should help the person cool off in whatever way possible until paramedics arrive.

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