Effects of sunscreen on human skin's ultraviolet radiation tolerance.

Purpose: To observe the alteration ultraviolet radiation (UVR) of skin's tolerance after its exposure to the small dose of UVR under the protection of sunscreen.

Methods: Eleven subjects who applied sunscreen were exposed to 0.75 dose minimal persistent pigment darkening (MPPD) and minimal erythema dose (MED) by the Phototherapy Unit for 4 weeks.