system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do forehead thermometers measure your internal temperature? Wouldn't it just give the temperature of the surface of your skin?

We have forehead thermometers at work now, and I'm curious how the thermometer measures your internal temp? If I have a fever, but it's 10° outside and my face is frozen, wouldn't that affect the reading?
gpt
Your forehead is a spot where the flesh on top of the bone is very thin. Lots of little blood vessels(capillaries) in that area as well, so generally your skin temp on your forehead is really close to your overall blood temp.