thank you for sharing this information. clearly, these two valuable scientists are in disagreement, which reflects the controversy of the sun's effects issue. this discussion raises two questions in my mind: 1. what exactly does 'good sun protection' mean, as described by prof. holick? my understanding is he recommends getting unprotected sun exposure 15 mins. x 2 per week, and then put on sun screen or a lotion? if so, what kind of lotion, with what specifics? or is something completely different that he means? 2. what is the correct way of applying the sunscreen, as prof. gilchrest mentions?