The extract, topically applied, significantly reduced UV damage say researchers led by Paul Talalay from the John Hopkins University School of Medicine, Baltimore. Furthermore, treatment with broccoli extract appears to have a long-lasting effect that continues long after the extract itself has disappeared from the system. The important chemical in the extract is sulforaphane, which differs from conventional sunscreens in that it does not absorb the UV rays. Instead its protective qualities lie in its ability to upregulate the cells' own defenses against UV damage. This defence system includes a network of cytoprotective (cell protective) proteins that help protect against the damage caused by a wide range of toxins and carcinogens. Protective mechanisms evoked in cells by the sulforaphane include inhibition of the activation of procarcinogens (inactive carcinogens that can be activated when in the organism), disposal of damaged and potentially neoplastic cells (cells that proliferate without control) by cell cycle arrest and programmed cell death, and the suppression of inflammatory responses. The team measured erythema, the reddening of the skin which can be caused by UV radiation, as a marker for evaluating the damage caused by UV radiation. Sulforaphane-containing broccoli extract was applied to defined areas of subjects' skin on three consecutive days prior to UV exposure. The protective effect was calculated from the fractional reduction in erythema upon treatment, as responses to UV radiation vary greatly in individuals. The team found that the mean reduction in erythema by broccoli extract was 37.7 per cent. In addition, the study suggested that treatment with broccoli extract has a long lasting effect, although the sulforaphane does not remain in the tissues for more than a few hours. Subjects who were treated with the extract on three consecutive days, but were only exposed to UV radiation 48-72 hours after treatment, still displayed a significant reduction of erythema. This finding supports the hypothesis that sulforaphane's protective qualities are due to its ability to upregulate the longer lasting proteins of the cell's innate protective system, which continues to work long after the extract has been removed from the system, and not by absorption of UV rays. The researchers claim that such long lasting effects have not been demonstrated in either conventional sunscreens, or other protective substances such as lycopene.