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For babies, you'll get the most precise reading using a digital rectal thermometer; you can switch to an oral one when your child turns 3. An ear thermometer, although it's fast and convenient, can actually be deceptively tricky to use: You have to place it correctly in the ear canal for an accurate result. (Too much earwax can throw off the reading as well.) Underarm and pacifier varieties are also less reliable than the gold-standard rectal and oral thermometers. Also, be sure to ditch your glass thermometer. Those old-school thermometers contain mercury, a potent toxin that affects the brain, spinal cord, liver, and kidneys, and can cause learning disabilities. If it breaks, you risk exposing your family to mercury's harmful vapors. Still have one lurking in your medicine cabinet? Don't just toss it into the trash. Take it to your pediatrician (she can dispose of it safely), or drop it off at your local hazardous-waste collection site. --Avery Hurt
Originally published in Parents magazine, October 2007. Updated 2009
The answers from our experts are for educational purposes only. Please always refer to your child's pediatrician and mental health expert for more in-depth advice.