This time frame applies to daylight saving time; in standard time, you should try to avoid the sun between 9 a.m. to 3 p.m. You should protect your skin whenever you are out in the sun, no matter what time of day or time of year, winter or summer. Protect yourself in any type of weather: The sun's ultraviolet rays can reach the earth even on cloudy or hazy days. The rays also reflect off any surface, including water, cement, sand, and snow.

Ultraviolet rays are an invisible form of radiation streaming from the sun. There are three ranges of UV ray lengths: UVA, UVB, and UVC. UVA is the most abundant; this form can penetrate past the top layer of skin. Researchers believe that UVA can damage the body's connective tissue, boosting a person's risk for developing skin cancer. Much of the UVB rays are absorbed by the ozone layer in the earth's atmosphere. The UVB rays that do reach your skin can be damaging, even though they don't penetrate as deeply as UVA. UVC is very hazardous to the skin, but fortunately, all of these rays are absorbed by the ozone layer.

When possible, avoid outdoor activities during the middle of the day, when the sun's rays are most intense. If you must be outdoors then, wear protective clothing, a wide-brimmed hat, and wrap-around sunglasses that block 100% of UVA and UVB rays. Wear sunscreen and lipscreen rated with at least SPF 30. Look for sunscreens that block both UVA and UVB rays.

Exposure to UV rays is the key factor in the development of skin cancer. UV radiation also has been tied to the development of lip cancer (a form of skin cancer) and is associated with cataracts and other eye conditions. UV radiation also can lead to premature aging of the skin and abnormal changes in skin texture.

The UV Index was developed in 1994 by the National Weather Service and the Environmental Protection Agency. It gives a forecast of the expected risk of exposure to UV rays and recommends what degree of caution you should take when outdoors. The range given now follows the Global Solar UV Index: from 1 (low risk of exposure) to 11 and higher (extreme risk of exposure). The UV Index takes into account clouds and other local conditions that affect the amount of UV radiation reaching the ground. You can usually find the UV Index on your local newspaper's weather page.

Chemicals that cause a reaction with exposure to UV light (photoreaction) are called photosensitizers. Medicines and other products can cause photosensitivity. After exposure to UV radiation either from natural sunlight or an artificial source such as tanning booths, these photosensitizers cause chemical changes that increase a person's sensitivity to light. They can also cause exaggerated sunburn-like skin conditions. It's not clear whether sunscreens help protect against photosensitivity. The best protection is to stay out of the sun, but health professionals still recommend using sunscreen and protective clothing if you have to go outside.

It doesn't matter what form of sunscreen you use. What's important is that it blocks both UVA and UVB rays—this is called broad spectrum—and has an SPF of at least 30. Special sunscreens are available for sensitive skin and for babies.

The physical and chemical parts of sunscreen interact with the UV rays to protect your skin. You should always use a sunscreen with an SPF of at least 30. The higher the SPF number, the greater the protection. Even with a sunscreen, you should still limit the time you spend in the sun and take other protective measures, such as staying in the shade and wearing protective clothing, wrap-around sunglasses, and a broad-brimmed hat.

To be protective, clothing must cover as much of your skin as possible. If wearing long pants and a long-sleeved shirt isn't practical, at least wear a T-shirt and sunscreen of at least SPF 30. Dark-colored clothing appears to offer more protection than light-colored clothing. Dry clothes offer more protection than wet clothes. Certain brands of clothing have sun protection added to them. They are labeled with UV protection factor ratings.

This type of hat provides shade for your face, ears, and back of your neck. A straw hat isn't as good as a canvas hat, particularly if the straw hat has holes that let the sunlight through. If you wear a ball cap, cover up your ears and back of your neck or use a sunscreen with at least SPF 30.