The article outlining this recipe, to be fair, did not claim to cure dandruff (though the headline did). What I think the recipe was really for was a sort of smelly moisturising balm that would pretty much lose any effectiveness as you had to wash it out TWICE after half an hour. Well, that was a waste of an afternoon, then.
What causes dandruff?
There are two broad types of "dandruff" conditions, where the skin is irritated, itchy and flaky: dermatitis and psoriasis.
Scientists generally believe dermatitis, or if your head is oily, seborrhoeic dermatitis, is caused by a type of yeast or fungus from the Malassezia family that feeds off the sebum in your scalp. The fungus is pretty hardy and rubbing random herbs or other natural things found in your refrigerator with supposed antibacterial qualities on it in the hope of making it go away is no good at all. The yeast feeds on fat, so using an oil based natural, herbal tincture to try and battle your infection is pretty hopeless.
All main brand dandruff shampoos (such as Head & Shoulders or Nizoral) use tested antifungal ingredients which kill the fungus. The two most common anitfungal agents used are pyrithione zinc (used in Head & Shoulders) and ketoconazole (used in Nizoral). These agents target different types of Malassezia yeast, so if one brand doesn't work for you, try using the other to see if you get a better result.
Tea Tree oil (melaleuca) has also shown some effectiveness in killing a range of types of yeast, however, there are to my knowlege no commercial shampoos with enough of the extract to really be effective. A lot of the references to tea tree oil I've seen to date on shampoo bottles is pure marketing fluff.
You can purchase pure tea tree essential oil, however it is poisonous and should not be swallowed. Using tea tree oil on your skin can cause severe skin irritation including rash and blistering. Harsh stuff for a natural cure. You have been warned.
This condition is less common and completely different from dermatitis. Usually there are well-defined, hard silvery patches or plaques. These can often be ring shaped and red at the edge. The flakes sometimes come away in large sheets.
Psoriasis isn't very well understood. Current thinking is that it is caused by an auto-immune disorder, and groups of skin cells just start rapidly reproducing. There is no cure, but the two most favoured treatments are coal tar extract and UV (ultra violet light) treatment for more intractable cases.
Coal tar extract works by slowing down the production of skin cells. Shampoos such as T-Gel or lotions such as Exorex are available without a prescription at most chemists and can be effective for many people. If your condition doesn't respond to these treatments, you can be eligible for light, or phototherapy, treatment on the NHS. There are considerable side effects to phototherapy as the UV exposure can rapidly damage and age your skin, so do give the shampoos and lotions a good chance first.
Again, given that the condition is related to your immune system being out of whack, rubbing some herbs in your hair is honestly not going to help one bit.
Phew. I'm glad I got that all off my chest. At least until I come across another screwy cure for dandruff ...