Pallor is an abnormal loss of skin or mucous membrane color. It can develop suddenly or gradually, depending of the cause. It needs to be properly distinguished from other symptoms such as whitening of the skin or hypopigmentation (loss of skin pigment).
Unless it happens accompanied by pale lips, tongue, palms, mouth and other regions of mucuous membranes, (that is, a general pallor) it is probably not clinically significant and does not require any treatment. Pallor is more evident on the face and palms.
It is also important to notice that pale skin doesn't necessarily indicate disease — lack of sunlight or inherited paleness may be the reason, and it's nothing to worry about.
Some possible causes of pallor are: