A study of physical light screening agents.

In those photodermatoses in which the action spectrum involves wavelengths outside the short ultraviolet (i.e. is greater than 320 nm) little protection can be obtained against long UV (is greater than 320 nm) by the application of chemical light screening agents. An action spectrum involving wavelengths is greater than 320 nm is a common occurrence and may necessitate the additional provision of protection from a physical light screening agent. Such a physical agent is titanium dioxide and in a study of its use in a variety of formulations using in vitro techniques it was shown to be effective throughout the wavelengths 400-700 nm. It was also shown to have a satisfactory protective capacity in those photodermatoses in which the action spectrum involves wavelength peaks 365 nm (335-395 nm) and 400 nm (370-430 nm). It also has a reasonable cosmetic acceptability provided care is taken to incorporate in the formulations colouring agents which can be varied to suit the individual patient.