What is the difference between acne and rosacea?

[Guide]

For a long time, as noted by the late late Dr. Albert Kligman, rosacea was referred to as 'Acne Rosacea', which he said, "It is interesting that the original term for rosacea was "acne rosacea”, which has more features in common with acne than currently realized. If the “acne” portion had been retained in the later works, rosacea might have received much greater investigative attention." [1] 

So what is the difference? 

ANSWER (members only)