My face turned yellow when I took pictures. Why?

Usually due to white balance error. To put it bluntly, white was shot in a yellowish color, so it seems that the whole photo is warm, and the face is no exception.

White balance error generally has two reasons:

The first is that the ambient light is really yellow, such as a room lit by incandescent lamps and a scene lit by sunset. In this obviously yellowish environment, even if the camera adopts automatic white balance, it cannot be automatically corrected. You need to adjust the white balance manually. Of course, sometimes the photographer pursues such a tone, and there is no need to "correct".

The second is that you set the wrong white balance and made the original normal tone warm (generally, automatic white balance will not have this problem). This is a technical error. Just study the camera manual.

No matter what the reason, as long as it is not against the sky, such a white balance problem can be solved by later retouching. If it is a RAW file shot by SLR, it can be repaired without loss, even JPG files can be repaired quite well.