Natural Cures for Dandruff

My husband has had a bad case of dandruff or psoriasis or something like that for a long time. We tried a lot of cures like rubbing oil on his scalp before going to the sauna, rinsing with ACV, a milder shampoo and the only thing that seemed to help was toasted sesame oil which I can't find easily here in France. Still, we have discovered that although everything seems to work the first day after that his hair would be covered in dandruff again. Now we use mustard oil before the sauna, wash with the mild shampoo and rub a bit of coconut oil every morning and evening. He also washes his hair less often and so far so good! The coconut oil seems to keep his scalp moist and therefore free of dandruff!