To complement more reliable methods of reducing skin exposure to ultraviolet (UV) radiation (such as sun avoidance, clothing, and hats) sunscreen can be very useful. However, limitations to the effectiveness of sunscreen include the following common user errors:
Failure to apply enough
Uneven application / missed spots
Failure to re-apply
Because some amount of UV radiation might pass by the sunscreen, unintentional sunburn can occur. Think of these products as a back-up to other, more effective, sun safety strategies.