With any luck, you already have a thermometer because lately they are as hard to buy as toilet paper. But getting a second thermometer is optimal if someone in your household has covid-19 symptoms, says Michael Hochman, an internal medicine physician and director of the Gehr Family Center for Health Systems Science & Innovation at Keck Medicine at the University of Southern California.
If you’re in the market, an inexpensive, easy-to-use digital thermometer is fine, experts say — the no-frills type in drugstores and supermarkets for under $20.
“The accuracy is not based on how much it costs,” says Gary L. LeRoy, a family physician in Dayton, Ohio, and president of the American Academy of Family Physicians.
For adults and children age 4 and older, oral temperature taking is most popular. Rectal thermometer readings are more accurate, researchers found, but the slight outcome difference is not significant for ordinary use.
Some basics: Before each use, wash your thermometer in cool water. Then wipe it down with rubbing alcohol and rinse again. Don’t eat or drink anything hot or cold for at least five minutes before placing the thermometer under your tongue. Recently being out in the cold or heat or in a hot tub could also throw off a reading, as could vigorous exercise.
Remember to keep your mouth completely closed and breathe through your nose during the 30 to 40 second reading. When finished, clean the thermometer again with water and alcohol. Use a towel when you put it away or hand it to someone, Hochman suggests.
Rectal thermometers are advised for children up to age 3. To take rectal temperatures, use water-soluble or petroleum jelly for lubrication and insert the thermometer no more than a half-inch into the rectum. Never use the same thermometer for taking oral and rectal temperatures, LeRoy says.
Ear thermometers aren’t as precise as oral or rectal readings but acceptable for adults and children older than 3 months. Armpit temperature-taking is the least accurate and should be avoided unless it is the only option, LeRoy says.
Mercury thermometers? LeRoy scolded me when I confessed that’s all I have. OK boomer. While they work, these thermometers were phased out in 2011. If the glass cracks, mercury exposure is hazardous. If you own one, you are advised to surrender it and follow hazardous waste disposal recommendations where you live.
Now for the numbers. Conventional wisdom is that 100.4 degrees signals fever. “Normal” varies, however, and ranges from 97 to 99.5 degrees in people. Women tend to have higher temperatures than men, older adults typically run lower. Rectal and ear readings are usually higher than temperatures taken orally.
Your temperature can change as much as a degree depending on the hour, too — lowest in the morning and increasing throughout the day. “If you are 100.4 degrees in the morning, that’s a real fever,” Hochman says. But if your temperature goes up in the afternoon or evening, that’s “natural variation” he says, and doesn’t mean you are sicker.
“Don’t make yourself crazy by taking your temperature more than two to three times a day,” Hochman adds for those with symptoms. The thermometer provides one piece of information, he stresses. He is more worried by someone who appears ill or confused than a number on a thermometer.
LeRoy points out that a low reading does not guarantee you are fine. “You could be in a chilling phase of the fever,” he explains, when the body is trying to reset its temperature. Recheck your temperature from time to time if you are not feeling well, he says.
When to call a doctor about fever? “You can be febrile for several days without being alarmingly ill,” Hochman says. With covid-19, it is the cluster of symptoms with fever that are concerning — a dry cough, shortness of breath, fatigue.
“Use your judgment,” Hochman says. “Be guided by the overall picture.”