Dithranol or anthralin is a Hydroxyanthrone, anthracene derivative, medicine applied to the skin of people with psoriasis. It is available as creams, ointment or pastes. Dithranol has a slower onset of action in controlling psoriasis, typically several weeks, compared to glucocorticoid steroids, but is without the potential for rebound reaction on withdrawal. It cannot be used on the face or genitalia. There is some tentative evidence that anthralin might be useful for alopecia areata.

It temporarily stains the skin a yellowy-brown and permanently stains clothing fabrics and other materials such as ceramic sinks. It may cause a local burning sensation and irritation; this may be minimised by careful attention to the details of treatment and only gradually stepping up through the strengths of dithranol formulations. The surrounding skin can be protected using soft white paraffin and the treated area is covered with tube gauze.

Dithranol accumulates in mitochondria where it interferes with the supply of energy to the cell, probably by the oxidation of dithranol releasing free radicals. This impedes DNA replication and so slows the excessive cell division that occurs in psoriatic plaques.

Formal Chemical Name (IUPAC)
1,8-Dihydroxyanthracen-9(10H)-one

References

https://en.wikipedia.org/wiki/Dithranol