n technical terms, sunburn is an acute cutaneous inflammatory reaction that occurs usually between 1–24 hr after sun exposure.1, 2 The severity of the sunburn depends on two variables: the intensity or dose of light, and the length of exposure to the ultraviolet radiation (UVR). This reaction is characterized by different degrees of erythema frequently associated with pain, swelling and even the presence of blisters.2–4 Furthermore, exposure to excessive doses of solar radiation induces both acute and chronic damage to skin. However, these effects can be blocked by both UVA and UVB sunscreens. The present article therefore reviews mechanisms of UVR insult to the skin and provides sunscreen formulation suggestions for the development of sunscreen products to protect against this damage.
Photodamage and Skin Aging
Exposure to solar radiation causes sunburn, edema, premature aging expressed as wrinkles and fine lines, telangiectasia (spider veins), elastosis (leathery appearance), laxity, age spots (lentigos/freckles), seborrheic keratoses, actinic keratoses (precancerous scaly lesions) and skin cancers (basal and squamous cell carcinomas and melanoma).5–9 At the cellular level, solar radiation can produce adverse structural and functional changes in membrane proteins and lipids, chromosomal and mitochondrial DNA, and in immunocompetent factors.6–9 The source of these damaging effects is radiation in the ultraviolet range; specifically ultraviolet B (UVB), 290–320 nm; and ultraviolet A (UVA), 320–400 nm.5–9