Sunscreens are used to protect the skin from harmful effects of ultraviolet (UV) light but they do not completely prevent photocarcinogenesis, photoaging and photoimmunosuppression. They are useful for protection against UVB and short-wave UVA. Complete protection against long-wave UVA has not been achieved. There is no universally accepted method to evaluate UVA protection. Sun protection factor is a simple and internationally used method to compare sunscreen protection against UVB induced erythema. Adverse reactions to sunscreens are not common but they should be considered especially in persons with pre-existing eczematous conditions or photodermatoses. The use of sunscreens has increased steadily over the last decade; as a result, allergy and photoallergy to UV filters are now more frequent than in the past. Sensitization can occur from the various sunscreening agents and from the excipients included in formulations. An overview of sunscreens, their effectiveness, and adverse reactions is presented.