I'm a sufferer (male) of many years and I control it in the following ways:
Selsun shampoo 2.5% selenium sulphide (from boots or most pharmacies)
Solgar zinc picolinate 22mg
Witch hazel
Tea tree oil
Wet affected area of face and apply selsun. Don't overdo the shampoo, it can be quite runny in consistency but you only need a layer. Leave on for 3 or 4 minutes. Rinse with warm water, followed by cold. Pat dry. Apply twice in first week and twice in second week. This ought to bring very good results (often within a couple of days) After that try to limit him to using it once a week, or when it starts to get a bit red and sore and bothers him again.
Use a cotton pad once or twice a day to apply the witch hazel, which you can buy cheaply in savers. Add 5 or 6 drops of tea tree oil to the full bottle before the first time you use it. Try to get organic tea tree, but it will last ages coz you literally only put a few drops into a bottle of witch hazel. Don't use tea tree neat on the face! This mixture will help each day to keep redness, scaling and irritation down, a kind of maintenance of the selsun treatment.
It needs to be zinc picolinate and not just any old zinc supplement. The picolination ensures it's properly absorbed. Take one tablet and cut into sixths with a sharp knife. He should take one sixth a day with some water or juice and NO MORE, as it's inadvisable to ingest more than 3 or 4mg of zinc supplement a day. We get a lot from food, but those with dermatitis benefit from a minimal daily supplement.
One of my biggest triggers is carrots, would you believe. Beta carotene, in fact, which is an additive in lots of things. Generally it's worth watching what he eats to notice what makes him flare up.
A word of advice: try absolutely everything else you can think of before going down the steroid creams/ointments route. Not good.
Hope this helps. Let us know how he gets on 