The National Weather Service (NWS) and the Environmental Protection Agency (EPA) developed the Ultraviolet (UV) Index in 1994. The UV Index is a useful tool to help the public take steps towards reducing UV radiation exposure, since skin cancer and other skin diseases have increased significantly in the US since 1975.

The UV Index tells us the level of UV exposure expected on a given day. The categories are: low, moderate, high, very high, and extreme with corresponding index numbers 1-2, 3-5, 6-7, 8-10, 11+. The UV Index reminds people to protect themselves when engaging in outdoor activities.

The EPA encourages consumers to practice the following sun protection steps:

• Check the UV Index for the UV forecast.
• Limit exposure during midday hours.
• Seek shade.
• Wear clothing made from tightly woven fabrics. UV rays can pass through holes and spaces in loosely knit fabric. Long-sleeved shirts and pants are recommended.
• Wear a hat with a wide brim that protects the eyes, face, and neck.
• Wear sunglasses that provide 100% UV protection.
• Use broad spectrum sunscreens with at least Sun Protection Factor (SPF) 15 and reapply regularly. Remember to apply sunscreen on any part of the skin that is exposed to the sun, such as the nose, the back of the neck, and the rims of the ears. Use lip balms or creams containing sunscreen.

Here’s the chart straight from the EPA:

New EPA UV Index Guidelines

So, you might be wondering how is the Index calculated?

In a nutshell, it begins with forecasting the total ozone amount by using NWS models. Then, the sun angle for that specific day is determined. Next, a radiation model determines different UV radiation wavelengths, which are then weighed into human skin. Lastly, outside factors such as location, sea level and cloud conditions are measured and adjusted to the index.

The UV Index is a great tool to educate yourself on how intense each day’s sun exposure will be. The sun can be extremely harmful, as most of us know, causing anything from wrinkles, to eye damage, to skin cancer. It’s great to have this kind of knowledge in order to prevent these things from happening to you.

Well, sunscreen contains chemicals that protect your skin by absorbing and reflecting UV ray and allows a certain range of UV light to be absorbed into the skin. It helps protect against UVA and UVB rays.

On the other hand, sun block contains physical ingredients that reflect and scatter the UVB light and acts as a wall between your skin and the sun. This is a better choice for you if you have sensitive skin.

The bottom line – most lotions are a combination of both sun block and sunscreen, so read the fine print to know what you are putting on your skin. Also, be sure to look for sunscreen or sun block that does not have vitamin A, retinol or retinyl palmitate which might break down in sunlight to photomutagenic compounds.

If you were born before the 1980s, you probably remember the old coppertone billboards. A cute little kid and a feisty little dog making it clear that a “healthy tan” and a nice “copper tone” were the goals of the summer sun season. No self respecting kid wanted to let their mom smear a gob of white, pasty zinc oxide on his nose. We didn’t even call it sunscreen in those days, we called it “suntan lotion”, and your sister might have even smeared on baby oil to amplify the suns effects.

It turns out that George Hamilton was wrong, and your mom was right.

Here are some things to keep in mind regarding sunburns:

• There is no such thing as a “healthy tan.” Unprotected sun exposure causes premature aging of the skin.
• Sun exposure can cause first and second degree burns.
• Skin cancer usually appears in adulthood, but is caused by sun exposure and sunburns that began as early as childhood.
• You can help prevent skin cancer by protecting your skin and your children’s skin from the harmful rays of the sun.

The first step to treating your sunburn is to avoid any exposure to the sun while in the healing process. The best treatment for sunburn is time since most burns heal within a couple of weeks. However, there are medical treatments such as aspirin, nonsteroidal anti-inflammatory medications (NSAIDs), moisturizers, and compresses.

Another interesting thing to note about sunburn is that is happens on more than just your skin, but also your eyes and lips. The eyes are very sensitive and need UV protection which can be provided in sunglasses. UV light can also cause pterygium and cataracts. The lips can be burned and blistered if overexposed to the sun. The best prevention is to apply a lip balm, such as petroleum jelly, that has an SPF.

So what is Ultraviolet Radiation (UV) anyways?

Ultraviolet (UV) radiation is that section of the electromagnetic spectrum between x rays and visible light, i.e., between 40 and 400 nm. The UV spectrum is divided into five classifications.

• Vacuum UV (40-190 nm)
• Far UV (190-220 nm)
• UVC (220-290 nm)
• UVB (290-320)
• UVA (320-400 nm).

The sun is our main natural source of UV radiation. Manmade sources include tanning booths,mercury vapor and halogen lamps,fluorescent and incandescent lighting, black lights, germicidal lamps,and certain lasers. Depending on the wavelength range of the emitted UV radiation, each source caries its own unique risks..

The atmosphere absorbs almost all Vacuum UV, Far UV and UVC so they are almost never observed in nature. The most common sunburn risks are the result of UVB. It has enough energy to cause damage to cellular DNA, yet not enough to be completely absorbed by the atmosphere. Individuals working outdoors are at the greatest risk of UVB effects. Most solar UVB is blocked the atmosphere, but that absorption varies by time of day, season, weather and other environmental factors.

The best defenses against sunburn are moderating your time in the sun and using proper SPF rated sunscreens and sunblocks to protect your skin when you are exposed.

This is definitely not true because sun exposure is not constant.  The intensity of the sun increases and decreases depending on the time of day, which makes it hard to rely on an SPF number to prevent skin damage. Obviously, various factors come into play that determines how much sun a person is exposed to such as skin type, amount of sunscreen applied, and reapplication frequency.   Therefor SPF does not reflect time you can spend in the sun, but rather, is an imperfect and relative measure of how much protection is provided by particular sunscreen lotions.
The second question that itches our brains is why do we need SPF?   We have been taught that the sun is friendly; that is provides us with warmth and is a good source of Vitamin D.   On the other hand, the sun is the source of ultraviolet  radiation, which can lead to permanent skin damage and cancer.

There are 3 different types of UV based on their wavelengths: UVC, UVB, and UVA. The 2nd and 3rd type,
UVB and UVA, have been proven to be very damaging to skin.  They are known to cause wrinkles, lowered immunity, aging skin conditions, and lastly, skin cancer.
A main functionality of sunscreen or sun block is to reflect or absorb these UV rays and prevent them from entering our bodies, protecting us from sunburn and other skin damage.  According to the EPA, a sunscreen with an SPF factor of 15 will screen 93% of the UVB radiation from reaching the skin while an SPF of 30 only increases the screening effect to 97%.   As you can see in the attached graphic,  lowering the SPF below 12 brings a significant drop in protection.  On the flip side, moving beyond an SPF of 20 brings almost no gain in skin protection.  You can read more about sunscreen and SPF in the  epa sunscreen guide .

How does it work?

The physical compounds titanium dioxide and zinc oxide reflect, scatter, and absorb both UVA and UVB rays. These ingredients, produced through chemical processes, do not typically cause allergic reactions. Using new technology, the particle sizes of zinc oxide and titanium dioxide have been reduced, making them more transparent without losing their ability to screen UV.  Some broad spectrum sunscreens   contain a number of chemical ingredients that also absorb UVA  radiation such as   UVA-absorbing avobenzone or a benzophenone (such as dioxybenzone, oxybenzone, or sulisobenzone)

In rare cases, these sunscreens with PABA or other benzophenones may cause  skin reactions, including acne, burning, blisters, dryness, itching, rash, redness, stinging, swelling, and tightening of the skin. Consult a physician if these symptoms occur.  Some sunscreens also contain alcohol, fragrances, or preservatives, and should be avoided if you have skin allergies.  You can read more about sunscreens in our sunscreen features here.