Psoriasis is a common, chronic, inflammatory skin disorder. This invention provides the use of a compound of formula (I) R—CO—X (Wherein R is a C16-24 unsaturated hydrocarbon group optionally interrupted α, β, γ, or δ to the carbonyl group by a heteroatom or group of heteroatoms selected from S, O, N, SO, SO2 said hydrocarbon group comprising at least 5 non-conjugated double bonds; and X is an electron withdrawing group) in the manufacture of a medicament for the treatment of psoriasis.