Conjunctivitis means the white part of the eye ball becomes pink or reddish. Conjunctivitis is an infection of the transparent membrane that eyelid and covers the white part of the eyeball.
The skin under the eyes is very thin, so the nerves are visible. When blood flow in these nerves is rapid, it appears to be deeper than the outside, due to which the dark circles are seen. In some people, the eyes are blown inwards in such people, there are dark circles.