Skin cancer — the most common kind of cancer in pale-skinned folks across many different parts of the world — is on the rise. With it, so are skin cancer deaths.  Ultraviolet radiation from the sun, which damages your DNA, is the prime cause of skin cancer. While the sun's UV rays have always been damaging, data from NASA shows that the amount of UV radiation that reaches the Earth, and hence your skin, has been increasing over the last three decades. 
What Do The Sun's UV Rays Do To Your Health?
Excessive exposure to UV radiation can affect your whole body:
- Skin cancer is a major risk: more than two million non-melanoma skin cancers occur across the globe on an annual basis, along with around 200,000 cases of malignant melanoma. Malignant melanoma is the most dangerous skin cancer. Pale-skinned people, especially those of Caucasian decent, have the highest risk of developing it.
- Being in the sun a lot causes premature wrinkling.
- Your eyes can be damaged by sun exposure as well. Cataracts, which can lead to blindness, are just the start.
- Excessive sun exposure weakens your immune system, leaving you more vulnerable to infections. 
Heat stroke and sunburn are two immediate risks of excessive sun exposure. Your risk of skin cancer goes up each time you have a sunburn — at any age, not just if it happens in childhood. 
Your Ultraviolet Radiation 'Thermometer': Check The UV Index
The sun emits different kinds of radiation, the main forms of which are visible light, infrared radiation (which we feel as heat), and ultraviolet radiation. If you check the temperature and peek outside to see how bright it is before deciding whether to wear a sunscreen and sunglasses, you're missing part of the picture — UV radiation can neither be seen nor felt, and its intensity does not actually depend on how hot it is outside. (The UV index does depend on factors such as how cloudy it is, what the ozone coverage is like, the altitude and latitude at which you live, and the time of day; the midday hours are always the riskiest.)
The UV index exists on a scale from one to 11+, one meaning "low UV exposure", and 11+ representing "extreme UV exposure". You should always take care to protect yourself against the sun's harmful rays, but the higher the UV index, the more important it becomes to take protective measures. If the UV index is eight or higher, you're advised to stay out of the sun altogether between the most intense hours of 11 am and 4 pm.
Some media use the UV index to report "burn times", or the duration of time you can spend in the sun without burning, but the US Environmental Protection Agency warns against this. People have different burn times depending on their skin color, after all, and skin sensitivity also varies. 
Taking Appropriate Protective Measures To Stay Safe In The Sun
You're advised to use a sunscreen with a sun protection factor of at least 15. Note that you don't get double the sun protection if you use SPF 30 as opposed to SPF 15 — SPF 15 filters out around 93 percent of UVB rays, while SPF 30 protects you against 97 percent of UVB rays.  Research shows that young white Europeans tend to stay in the sun for longer if they use a sunscreen with a higher SPF. Don't make this same mistake, as no sunscreen filters out all UV rays. 
What does help is choosing a sunscreen that is labeled as offering "broad-spectrum protection", because these sunscreens protect you against UVA rays — the kind mainly responsible for causing premature aging — as well as UVB rays. The efficacy of sunscreen wears off after about two hours, so you need to reapply it throughout the day. Apply sunscreen to all exposed areas of your body, and apply it liberally. 
When the UV index is between three and five, stay in the shade if you go out during midday hours (between 11 am and 4 pm), if it's between six and seven, minimize your time in the sun during these hours, and if the UV index is higher than eight, try your best to stay out of the sun altogether during these hours.
It's also best to:
- Wear sunglasses with UV protection
- Steer clear of bright surfaces such as light beaches, which are reflective and expose you to more UV radiation
- Wear clothes made from tightly woven fabrics, and choose long, loose, sleeves and legs if possible
- Wear a hat, especially if you don't have much hair
- Stay in the shade [5, 9]
But I Want A Tan, Though
Yeah, we understand — and you're certainly not alone. A survey conducted by the American Academy of Dermatology made it clear that teenagers are especially at risk of putting their health in danger for the sake of a tan:
- 63 percent of American teens believe they look better with a tan, and 59 percent think tanned people look "healthier"
- 43 percent admit to sunbathing
- 28 percent of teen girls and 14 percent of teen boys shockingly say they never use sunscreen 
If you want a safe tan, tanning sprays are your best bet. However, research, unfortunately, reveals that most fake tan users don't decrease their time spent in the sun  — don't fall into this trap!
Don't Shy Away From The Sun Altogether
While vitamin D can indeed be obtained from (a rare few) foods, it's also synthesized in the body as the direct result of exposure to sunlight. Vitamin D is crucial for human health — it's not just important to increase calcium absorption and keep your bones healthy, but also plays a role in the functioning of your immune system, in cell regeneration, and to reduce inflammation in the body. 
If you're vitamin D deficient, a lack of sun exposure is the most likely cause. Most white people only need half an hour in the summer sun in a bathing costume to get 50,000 IU of vitamin D, while most black people get between 8,000 and 10,000 IU from the same amount of sun exposure. Both more than meet daily needs. (Note that this form of vitamin D3 synthesis is especially important to vegans, who will only get D2 from their diet!) 
The Bottom Line
The sun's a pretty contradictory thing, isn't it? Without it, life on Earth simply wouldn't exist — but it also poses dangers galore, especially in the face of climate change. By using the UV index reports for your area to understand how intense the ultraviolet radiation is on any given day and adhering to the sun safety measures set out above, you can enjoy the benefits of moderate sun exposure without incurring the risks.