Irritant reactions to dithranol in normal subjects and psoriatic patients.

The irritant reaction to dithranol on normal forearm skin of forty psoriatics and forty controls was investigated by skin contact thermometry and ID50 values were calculated for each skin type (I to IV). We concluded that there is no difference between the irritant effects of dithranol in psoriatics and normal subjects. There was no correlation between irritant dose threshold and minimal erythema dose (MED) to ultraviolet radiation (UVR) but skin type I patients are the most sensitive. The irritant response to dithranol can be partially blocked by prior treatment with indomethacin.