Overexposure to UVlight induce redness and pain to the skin, and a sunprotection screen applied topically before exposure will ameliorate this reaction. It is likely that people change their sun bathing habits towards longer UV exposure when using sunscreens
I am not aware of any data showing the long term effects of the use of sunscreens,
In worse case scenario the likely change in sun bathing habits towards more intense exposure to UV might be the causation of the increased incidence of malignant melanoma we witness now 20/30 years after the introduction of sunscreens widely being used in the population.
Just a thought