A study of oil of bergamot and its importance as a phototoxic agent. II. Factors which affect the phototoxic reaction induced by bergamot oil and psoralen derivatives.

Using a standardized open photopatch test technique, the phototoxic reactions produced by bergamot oil bergapten (5-methoxypsoralen) the active component of the oil, and xanthotoxin (8-methoxypsoralen) were studied. The reaction was affected by a range of factors such as the vehicle (PMF or ethanol), the concentration of ethanol in the vehicle, the skin site, the interval between application of the psoralen and irradiation, the hydration of the skin, and the degree of natural or sun-induced pigmentation. Repeated photopatch testing at the same skin site produced an increase in sensitivity. Eye colour, natural susceptibility to suntanning, age, and sex, had no effect on the phototoxic response to psoralens.