It has been stated that the key to prevention of oral cancer is to avoid the "five Ss: smoking, spirits, spices, sepsis, and syphilis." There is certainly enough evidence to add another "S"--sunlight. Although there is a paucity of information in the dental literature on the use of sunscreens, the following dermatologic recommendation is noteworthy: "Persons with Skin Types I and II should never sunbathe and should adopt a program of daily application of effective sunscreens (SPF 15) as a habit and from an early age--in much the same manner as daily brushing of the teeth is adopted to prevent dental caries." The dentist should advise patients at high risk for squamous cell carcinoma and those with recurrent herpes labialis to use a sunscreen for the lips of at least SPF 15. The best sunscreen formulation at the present time is a combination of either PABA or an ester of PABA along with a benzophenone. A frequent combination seen on product labels is Padimate O and oxybenzone. Sunscreens should be used year-round on the lips with two applications 1 hour before sun exposure, and hourly reapplication while in the sun. If the convenience of a "lipstick" product is not important to the patient, then a skin product of the liquid or gel type should be used. If the appearance is not important, a white opaque cream containing titanium dioxide, talc, or zinc oxide may be used as a physical barrier. Women may use an opaque lipstick, but should first apply a chemical sunscreen of at least SPF 15.(ABSTRACT TRUNCATED AT 250 WORDS)