Exposure to sun rays, the real story

A science writer asked me this Q: If too much sunlight makes skin cancers dangerously likely their recommendation is to use the strongest sunscreen.. When they discover (what scientists had been trying to tell them from the start) that too little sun exposure is also a problem their first impulse is to pretend they have not heard. Why is this?

When I read the comments here like the one on sun's exposure, I feel people don't have a full picture to comment appropriately. A partial picture is being depicted here - most probably because of the partial picture media gives.
Yes, more of sun's exposure is extra bad for the white skin - and somewhat less harmful for dark and dusky skins and evolution has taken care that people who live at the equator have dark skins with melanin to face the wrath of the sun efficiently. That doesn't mean UV radiation is not bad for darker skins. But darker skins can fight it more powerfully than lighter skins.
So people with white skin should be more careful and their exposure to the sun should be only at dawn and dusk when the sun's rays will have good effect.When people go out during other times they should use full clothing, hats, umbrellas, sunscreen and sunglasses.

There are 3 main types of UV rays:

• UVA rays age skin cells and can damage their DNA. These rays are linked to long-term skin damage such as wrinkles, but they are also thought to play a role in some skin cancers. Most tanning beds give off large amounts of UVA, which has been found to increase skin cancer risk.
• UVB rays have slightly more energy than UVA rays. They can damage skin cells’ DNA directly, and are the main rays that cause sunburns. They are also thought to cause most skin cancers.
• UVC rays have more energy than the other types of UV rays, but they don’t get through our atmosphere and are not in sunlight. They are not normally a cause of skin cancer.

Both UVA and UVB rays can damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what’s known today, there are no safe UV rays.

The strength of the UV rays reaching the ground depends on a number of factors, such as:

• Time of day: UV rays are strongest between 10 am and 4 pm.
• Season of the year: UV rays are stronger during spring and summer months. This is less of a factor near the equator.
• Distance from the equator (latitude): UV exposure goes down as you get further from the equator.
• Altitude: More UV rays reach the ground at higher elevations.
• Cloud cover: The effect of clouds can vary. Sometimes cloud cover blocks some UV from the sun and lowers UV exposure, while some types of clouds can reflect UV and can increase UV exposure. What is important to know is that UV rays can get through, even on a cloudy day.
• Reflection off surfaces: UV rays can bounce off surfaces like water, sand, snow, pavement, or grass, leading to an increase in UV exposure.

The amount of UV exposure a person gets depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen.

UVA radiation (95–97% of the UVR that reaches Earth’s surface) penetrates deeply into the skin, where it can contribute to skin cancer indirectly via generation of DNA-damaging molecules such as hydroxyl and oxygen radicals. Sunburn is caused by too much UVB radiation; this form also leads to direct DNA damage and promotes various skin cancers. Both forms can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers. Excessive sun exposure can also cause cataracts and diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses.

 Radiation at the longer UV wavelengths of 320-400 nm, called UV-A, plays a helpful and essential role in formation of Vitamin D by the skin, and plays a harmful role in that it causes sunburn on human skin and cataracts in our eyes. The incoming radiation at shorter wavelengths, 290-320 nm, falls within the UV-B part of the electromagnetic spectrum. (UV-B includes light with wavelengths down to 280 nm, but little to no radiation below 290 nm reaches the Earth’s surface). UV-B causes damage at the molecular level to the fundamental building block of life— deoxyribonucleic acid (DNA). DNA readily absorbs UV-B radiation, which commonly changes the shape of the molecule in one of several ways. But living cells are “smart.” Over millions of years of evolving in the presence of UV-B radiation, cells have developed the ability to repair DNA. A special enzyme arrives at the damage site, removes the damaged section of DNA, and replaces it with the proper components (based on information elsewhere on the DNA molecule). This makes DNA somewhat resilient to damage by UV-B.

The sun’s UV rays increase a person’s risk of cataracts and certain other eye problems, too. They can also suppress the skin’s immune system. Darker-skinned people are generally less likely to get skin cancer than light-skinned people, but they can still get cataracts and immune suppression.

And you need not stay for hours in the sun to get the benefits. Just a few minutes' exposure is enough. More exposure is being done to get tan -from a beauty point of view not to make beneficial vitamin D!

Your body makes vitamin D when your skin is exposed to the ultraviolet B (UVB) rays in sunlight. About 10 to 30 minutes of exposure to the skin on your face, arms, back or legs (without sunscreen) two times every week is enough.

Use sunscreen on hazy or cloudy days too if you exceed this limit. A broad spectrum sunscreen is the most efficient one. Sunscreen products can only be labeled “broad spectrum” if they have been tested and shown to protect against both UVA and UVB rays. Some of the chemicals in sunscreens that help protect against UVA rays include avobenzone (Parsol 1789), ecamsule, zinc oxide, and titanium dioxide. Only broad spectrum sunscreen products with an SPF of 15 or higher can state that they help protect against skin cancer and early skin aging if used as directed with other sun protection measures.

The amount of exposure also depends on the time of the year and place where you are living. In the northern hemisphere, the UVB rays are more intense during the summer months and less intense during the winter months. In fact, if you live north of the 42-degree latitude, you'll have a difficult time getting enough sun exposure from November through February.

And for the body rhythms to work properly, you need not stand directly in the sun, just exposure to light standing in a shade will do.
That is the real picture media or science writers or communicators should be giving. It is not the fault of science if they fail!