Why is there a red dot on my iphone?

So i didn't notice till today that there's a red dot next to the front speaker under the camera on my 5s i've never seen it until today, i couldnt help but notice that when i don't touch the screen the light gets dim but when i do touch it the light, lights up again. I've read some reviews & some have said it shouldnt be able to be seen with the naked eye. Any help on what this little red dot is?

It's a proximity sensor.

So when you use the phone to talk to people, the phone's screen shuts off so that your face doesn't end up pressing buttons

Its normal. The iPhone 5S comes with an infrared sensor required while taking pictures from camera(for proximate sensing etc). It is usually so faint that it is ignored most of the times. But sometimes, due to the camera app (MAYBE! I'M NOT SURE) not being closed or apps like skype etc which req. Cam access are active. Or sometimes, some apps have bugs that leave the camera app working 24x7. Do you remember installing any apps before this happened? Try uninstalling them also and check if the red doot exists or not.

If not, you can go the Apple Service centre with the warranty slip for them to repair it for free or replace your iPhone 5S with a new one.