Our requirements for a thermometer are simple: It should be accurate, consistent, and available.
Whereas in previous years of research and testing we could be more selective (prioritizing additional criteria such as speed and features like large, backlit displays and options to disable sounds, among other things), in July and August 2020, during a pandemic that has upended commercial supply chains, we couldn’t afford to be as choosy. Like everyone else, we were limited to choosing from whatever was in stock at the time. We will continue to monitor the availability of our picks and other promising options.
Types of fever thermometers
Digital thermometers have made difficult-to-read mercury thermometers (also known as stick thermometers) obsolete. Digital models come in several formats—the key is to find a user-friendly thermometer that offers accurate and consistent readings with the least amount of discomfort.
While traditional oral/rectal/axillary thermometers have long been the most popular tools to take temperatures at home, forehead and ear thermometers tend to be faster and easier to use, especially with children.
Stick thermometers are simple and offer reliable measurements and fast results, but you need to keep your mouth closed around the probe for anywhere between 10 and 60 seconds, and oral measurements may be skewed if you’ve recently consumed something very hot or cold. Using a stick thermometer orally is tough for most toddlers and preschoolers, so such models are recommended for people ages 4 and up. Oral thermometers today usually pull triple duty as axillary (armpit) and rectal thermometers, as well. Although rectal temperatures have long been the gold standard for infants, many countries, including the UK, actively dissuade parents from using the oral or rectal methods at any age due to discomfort with the former and safety concerns with the latter (PDF). The UK now recommends that stick thermometers be used for armpit (axillary) measurements for newborns under 4 weeks and suggests using infrared forehead thermometers for any age above that. The American Academy of Pediatrics still recommends rectal thermometer use for newborns but acknowledges research that shows infrared thermometers are accurate for people over the age of 3 months old.
Ear and forehead infrared thermometers, both in-ear/on-forehead and contactless, are accurate enough to properly track a fever and are generally easier to use than stick thermometers. These thermometers tend to be a little more expensive than simpler oral/rectal/axillary models, but they’re worth the investment when speed and comfort are top concerns.
Forehead and ear thermometers both measure temperature based on heat radiated from either the temporal artery (forehead) or the eardrum (ear). Although it is tempting to just place an ear thermometer in an ear and press the button, these thermometers are a little more complicated than “insert and wait,” so make sure to follow the directions to pull out the shell of the ear to line things up. The Mayo Clinic does not recommend ear thermometers for newborns; Mayo advocates a minimum age of 6 months, basically when children are old enough to balk at a rectal thermometer but too young to manage an oral one.
Whereas ear thermometers almost always require skin contact, many forehead infrared thermometers are “no touch,” contactless models (others require a light touch of the thermometer to the forehead). On the downside, results from these thermometers may be affected by factors such as perspiration and air temperature (taking the temperature itself may not wake up the sick person, but wiping the sweat off their head first might). Infrared thermometers are also more susceptible to ambient temperature: To work properly, they need to be in the same room as the person who needs their temperature taken for around 30 minutes prior in order to acclimate to the surrounding air temperature and provide an accurate measurement.
Demand for contactless thermometers has skyrocketed this year. With a global pandemic of a highly transmissible respiratory virus ongoing and with restrictions in place, the idea of a no-touch thermometer is particularly appealing—as is the idea of taking a sleeping child’s temperature without disturbing them. Although the technology is still fairly new, it is being widely adopted in clinical, commercial, and household settings.
As early as 2014, the US government has used non-contact infrared thermometers (PDF) over other types, saying they are as accurate as contact thermometers while being low cost and easier to use. The Mayo Clinic now recommends infrared thermometers for infants 3 months and older and acknowledges recent studies (PDF) that show contactless, infrared thermometers to be reliable, including when used on newborns.
Most of the thermometers we tested covered a range from roughly 96 °F to 109 °F with an accuracy of ±0.4 degree. Some report lower accuracy at higher ranges, but if your temperature is pushing 107 °F, you’re probably in a hospital and not at home quibbling over a 0.4-degree difference.
Whatever type of thermometer you choose, it is important to remember that similar to a bathroom scale, no device meant for home use can provide exact, 100% accurate measurements. At-home fever thermometers are just not that precise (and temperature is not a static measurement). Luckily, this isn’t the goal: Just as how a bathroom scale is meant to track trends in weight gain and loss, a thermometer’s job is usually to track trends over time.