I had dermatitis on top of regular acne as a teen. Commercial products and the nasty alcohol based medicine a dermatologist gave me just made it worse!
What helped me was taking a rag and soaking it in hot green tea and washing my face with it, taking my time to also use it as a bit of a compress. Green tea is antibacterial and an anti-inflammatory.
After I was done, I would use a little of pure sesame seed or coconut oil to moisturize.
Of course, I wasn't the herbalist I am today, so now I would suggest collecting plantain and combining finely chopped handful of that with a cup of oil (blend of coconut and olive oil/sunflower oil) and empty the contents of 2-3 chamomile tea bags. Toss it all into a crockpot and let it sit on low covered for a few hours, stirring occasionally. Then strain, add about a teaspoon of vitamin E oil, stir and put it in the refrigerator. It lasts about 6 months as long as it is refrigerated and even works great as a salve on bruises and small cuts. If you don't like the smell, you can add something like roses or rosemary to make it more appealing.
The above recipe healed my acne scars which were old because I'm almost 30! It also shrinks pores which is usually a problem with those who suffer with skin problems.
Always double check any herb/oil on the inside of your wrist and wait an hour to see if there is a physical allergic reaction before using it. I'm allergic to ragweed but I'm okay with chamomile and plantain but others may not be. They are related!