Similar thing has been happening to me from BP - I've been putting it down to irritation really (but my face has always been reddish in comparison to my neck). Do you think that could be all it is for you? Have you been using Epiduo for long? If it's fairly new or if you've started using more of it recently - that could be why. Does Epiduo increase your sensitivity to the sun? (I'm guessing it does)That could be a factor too maybe - so a sunscreen could help (if you're not already using one).
To me it looks like it would go away if you stopped Epiduo but I'd assume that it would get better with time too... that is an assumption though as I haven't used Epiduo before. Hope someone else can give you some better advice / help!
Thanks for the reply Lilly! I guess it probably is irritation I just found it a little alarming! My face has always been slightly darker than my neck but never anything like this much. I've been using it for 2 weeks so yes it is fairly new for me, though I have used BP before when I was on the Regimen. I always make sure to wear sunscreen and I haven't been out in the sun much recently in any case. I really hope you're right and it will get better with time when my skin becomes more accustomed to the Epiduo!