When ultraviolet light hits your skin, pigment-making cells put out more pigment in an attempt to shield tissue from damage. The more UV light, the more pigment is produced as your skin tries to keep from burning. Over time, skin exposed to sunlight will develop wrinkles and age spots, and run the risk of skin cancers. Nobody wants to stay inside, and long sleeves and hats aren't always practical or comfortable. The trick is to find the right sunscreen for you, and to use it whenever you go out.
If you have fair skin and light hair, look for an SPF (Skin Protection Factor) of 15 or higher. Apply it generously to get all the protection it claims, and reapply frequently if you're sweating or in the water.
About three people out of a hundred have adverse reactions to certain sunscreens. Fortunately, there are several different kinds of chemicals used in sunscreens, and few people are sensitive to all of them. Read the labels before you buy, and test products on small patches of skin before applying them generally.
When you find a sunscreen that your skin can tolerate, you should use it every time you go outside, even on overcast days. Apply sunscreen to all exposed skin and even under loosely woven fabrics.
Cataracts are associated with chronic exposure to sunlight, so don't neglect your eyes. Sunglasses can be fashionable and expensive and still not provide adequate ultraviolet protection. Read the labels, and find a pair that filters at least 96% of UV rays.