Compare the advantages and disadvantages of the physical and chemical sunscreens. Physical sunscreens are agents that scatter and reflect UVR, while chemical sunscreens absorb UVR through a photochemical reaction. Physical sunscreens include zinc oxide and titanium dioxide and have advantages over chemical sunscreens. Physical sunscreens are inert, they do not break down over time, and they do not cause contact dermatitis or photodermatitis. They block both UVB and UVA (Table 49-2). However, physical sunscreens have one drawback: they leave a slight makeup base appearance to the skin that some people find unappealing. Although chemical sunscreens do carry a risk for contact dermatitis and photodermatitis, the risk is quite low (0.1% to 2.0%). Another disadvantage of chemical sunscreens is that they degrade with sun exposure, requiring reapplication every 2 hours. However, for many people, the advantages of chemical sunscreens outweigh the disadvantages. Chemical sunscreens are available in a plethora of formulations, such as creams, lotions, and gels. There are formulations for use on the face, lips, and small children. Today, there are chemical sunscreen formulations that block both UVB and UVA, and these formulations should be recommended to patients.
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