A NEW wristwatch that tells sunbathers when to cover up to prevent burning may give people a false sense of security, say dermatologists. Sunwatch II, a revamped version of an earlier design, will be launched in Britain this summer. It calculates the length of time bathers can be exposed to the sun without burning by considering time of day, type of skin and the sort of lotion used.

But Rona MacKie, Professor of Dermatology at Glasgow University, points out in General Practitioner that there is no such thing as a safe dose of sun and that all exposure is cumulative.